If you have emoji reactions, it’s a lot more difficult to show sympathy than simply sending a heart emoji. Because heart reactions usually mean “love this” or something (I don’t understand the full semantics of emoji reactions), and you’re supposed to use something else for sympathy.
I’m not sure how to explain this better, but the discords I do visit have a long list/dictionary of emoji reactions and what they’re used to mean. There are only a few discords like that, tho. (More specifically, I only know of exactly one.)
Generally speaking, a system with fewer reactions (twitter, github) is better than one with many (proprietary chat apps etc).