I "like" posts to show support.
emoji reactions would be really bad for me, because I'd need to choose an emoji that best describes my feelings. if you know anything about autistic ppl, you can probably see why that's a problem.
if I like your sad post, that's not me enjoying that you're sad, it's me showing I care.
if you post about a cool thing on the other hand, I like it because I think it's cool too.