[Cthulhu_]

Because there's criticism and constructive criticism; the one is easy, impersonal (in the form of downvotes or dislike buttons), and completely useless because it just goes "I don't like this" - or, in relatable terms, a Linus-ism of "This code is shit".

Instead, both the criticism-giver and the receiver are better off if you went "This code is shit, /because/ so-and so, and you can improve it in this-and-that way".

Of course, a "I like this /because/" is also more constructive than a "I like this". But I'm sure there's been plenty of examples that no matter how many "I like this"-es you get, it only takes one "this sucks, you suck" to demotivate someone.