Why do people think Miami has a tropical climate when it's North of the tropic of cancer and it freezes sometimes?

We have palm trees and and green grass and flowers everywhere. We have sunny warm beach days in February. Compared to the frozen north, that's plenty tropical. 

Because its a well known, most tropic-like location in the CONUS

Because a "tropical climate" is defined as "a non-arid climate in which the mean temperature is about 64°F throughout the year" Miami is certainly not arid and freezing can happen in a tropical climate sometimes if the average temperature meets the definition.

I suppose they are misinformed. Or uninformed. One of the two usually accounts for why people don't know things.