As a producer, Im gon have to say it has a lot to do with the overall MOOD that trap beats set. Ya'll keep labeling these types of beats as "trap", even when the nikkas on the track aren't even talking about trappin' (ex. I Dont Like). On every single beat you can rap about cocaine to, you can also rap about any subjects with a darker feel, like murder, ridin' around the city late at night, nikkas double crossin, etc. Basically anything that happens in the street can be rapped about over a "trap" beat.
Then there's those club bangers with "trap" influences, like No Hands, Racks on Racks, Cash Out, etc. These beats have all the same "trap sounds" that a typical trap record would have, but the producers arranged the melodies on these club tracks in a way that makes the mood go from daunting and provocative, to friendlier and more positive.
When I make a beat with some hard hitting bass, some hi hats, synths, strings, and horns, ya'll gon label it as trap and figure it aint shyt, but to me that beat is theme music for when you hop in the whip with the homies and its 1:00am and you just ridin around.