In the Bible, why would Paul get away without proving that he was a Roman citizen?

On “How could Apostle Paul prove his citizenship?”, we note that Paul proved his Roman citizenship by birth in a Jewish family in the city of Tarsus within the province of Cilicia (Acts 22:3) which was designated as a "free city" by Rome. And those born in free cities were granted citizenship.  (there's vast information available as to what constituted classifications of who could be a Roman Citizen.)  

Several reasons occur to me; for one:  For one thing people didn't necessarily walk around with their personal documents of citizenship - anymore than we do nowadays how many of us carry birth certificates, passports in our daily travels; especially if we are just going to a store.  We need to carry our license if we drive vehicles; so perhaps there was leniency as to when a person needed those documents presented in Roman life.

Note: Acts 16: 37-38:

37 But Paul said unto them, They have beaten us openly uncondemned, being Romans, and have cast us into prison; and now do they thrust us out privily? nay verily; but let them come themselves and fetch us out.

38 And the serjeants told these words unto the magistrates: and they feared, when they heard that they were Romans. (It was a very serious thing to arrest a Roman citizen and not grant him, his legal rights, which is why the magistrates became fearful.)  

More importantly, imagine the trouble he'd bring to himself had he lied, he'd been tortured to death had his statement been found falsified.  The Romans wouldn't have been merciful.  Also the Romans had no great admiration for the accusers of Paul; imagine the uproar they just caused; Paul's question immediately caused a penetrating silence to overcome them as they knew if he was being truthful they would be in serious trouble.  I imagine his making an appeal would legitimize his claim; to falsify that kind of information to any guard would jeopardize his life for certain as the Romans had zero tolerance for any non citizens of Rome claiming citizenship.  Paul would have incurred excessive brutal treatment, had he lied; perhaps death.  The jailers reactions seem valid to me; they stopped instantly due to the severity of this (Pauls) claim below.

 "Civis romanus sum" ~ powerful words in deed which every Roman noted instantly. 

" When Paul asked " "Is it lawful for you to flog a man who is a Roman citizen and uncondemned?" He drew the immediate attention of the prison officials. (see below for the full account.

The Latin phrase cīvis rōmānus sum (Classical Latin: [ˈkiːwɪs roːˈmaːnʊs ˈsũː]; "I am (a) Roman citizen") is a phrase used in Cicero's In Verrem as a plea for the legal rights of a Roman citizen.[1] When travelling across the Roman Empire, safety was said to be guaranteed to anyone who declared, "civis romanus sum".

In the New Testament book of Acts, chapter 22, Paul the Apostle, when imprisoned and on trial, claimed his right as a Roman citizen to be tried before Caesar, and the judicial process had to be suspended until he was taken to Rome:

"22 Up to this word they listened to him. Then they raised their voices and said, "Away with such a fellow from the earth! For he should not be allowed to live." 23 And as they were shouting and throwing off their cloaks and flinging dust into the air, 24 the tribune ordered him to be brought into the barracks, saying that he should be examined by flogging, to find out why they were shouting against him like this. 25 But when they had stretched him out for the whips,[a] Paul said to the centurion who was standing by, "Is it lawful for you to flog a man who is a Roman citizen and uncondemned?" 26 When the centurion heard this, he went to the tribune and said to him, "What are you about to do? For this man is a Roman citizen." 27 So the tribune came and said to him, "Tell me, are you a Roman citizen?" And he said, "Yes". 28 The tribune answered, "I bought this citizenship for a large sum." Paul said, "But I am a citizen by birth." 29 So those who were about to examine him withdrew from him immediately, and the tribune also was afraid, for he realized that Paul was a Roman citizen and that he had bound him."

Another thing to consider is the Apostles name change; Saul changed to Paul. Saul was his Hebrew name; Paul is his Roman name.It's unlikely he would have a Roman name if he wasn't a Roman.  None of the Pauline letters mention that Paul is a Roman citizen, but the book of Acts claims twice that he is (Acts 16:37-38, Acts 22:25-28). In the latter passage, Paul states that he was born a Roman citizen. His citizenship status is the reason he can successfully appeal to the emperor (Acts 25 to check this out).

Paul could also speak Greek, and travelled with Luke the Apostle, who also was highly educated and more in tune with a Romanized education; having a better education than that of their Jewish counterparts who  actually followed Paul to incite trouble towards him.  See:  Several passages in Acts describe Paul's missions to Asia Minor and the encounters he had with Diaspora Jews and with local gentile populations. In Acts 13–15, the Jews from Antioch and Iconium go so far as to follow Paul to other cities and to incite the crowds there to violence against him. Paul had already been stoned and left for dead once.[Acts 14:19] In Philippi, a Roman colony, Roman magistrates beat and jailed Paul and his companions on behalf of the Gentiles.(Acts 16:19–40)

Of course the answers you receive will reflect whether or not someone believes in the accounts in the Bible... of Paul, inclusive of his citizenship. Nor would Paul jeopardize the lives of those imprisoned with him.   The fact is the Romans took heed! As a Roman Paul could have appealed to Caesar himself; the magistrates knew the laws surrounding Citizenship.  

Good question; I learned some things; hopefully this answer resonates truth to you.

He used his Roman citizenship to avoid the harsher punishment. 

Scripture does not include every last detail of every event. Otherwise it'd be a multi volume encyclopedia. 

Because tales of paul.getting his @ss beat without any repercussions would have just been sad and pathetic, so he had to spice it up by making like he was secretly tricking them into feeling bad about it

Assumes facts not in evidence.