Why do some people say “warship” when they mean worship?

It's partly due to r-conditioning of the vowels, but that merger is very common in English. Linguists call it the horse-hoarse or north-force merger. There's an article on wikipedia, https://en.wikipedia.org/wiki/English-language_vow...

It's a simple mis-hearing. Or they think "wor" should rhyme with "or" and "for", which is not unreasonable.

I never heard anybody say it that way.  Where are you, by the way?

One is for atheists and the other is for Noah.

ask them not us....

Isn't it more the other way around? Most people pronounce War with more of an O sound than an A. Seriously. Try focusing on making an A sound with that word without sounding like you're from South Carolina.