I mean honestly, my personal opinion is with you, but to challenge this with a dash of critical thinking;
Mobb deep, despite how much I love them, essentially just takes "t t ch t t t ch t" and 70% of the times the similar kick pattern with the similar sound texture, and just plays diff samples that mostly have the same feeling. that's the whole story of them for at least the entirety of their first 12 13 years of existence. Same goes for almost every east coast song back then, at least the ones I heard. and I'm bringing mobb deep in first because well I've listened to them the most.
And yeah you could say the vibes kinda differed from artist to artist, but the drum patterns, the sound textures and the harmonic and melodic elements did differ due to the variety of sample sources, but even the core of the chord progressions were the same for the majority of the time, Especially when there wasn't any samples or the samples weren't complex.
Another thing is well, despite being annoyingly similar, trap beats or at least non-sampled beats could be considered more brave, for as soon as you develop an ear it's kinda easier to make boom bap beats that stand out than trap beats that stand out.
on another thought process, since everyone else is also making trap music and they are all trying to be something they ain't -a producer who can win a beat this! or a warzone-, they have to put up facades to kinda make up for their lack of experience. "Fake it till u make it" as mr fade once put it. maybe that could be an answer to why trap beats sound similar; maybe both beginner boom bappers and beginner trappers copy the waves of "trend" within producers, but the boom bap ones don't really strike the listeners as "copying everyone" since the samples themselves provide a sense of uniqueness to the product no matter what.
'i was thinking about doing the same thing',no shit, same as every single other trap producer ever.
