There are a couple reasons why Dislike button is generally frowned upon in some other forums from different games and devs. A couple examples that may include but not limited to:

1. If many people agree on a suggestion or topic, often times a "like" will suffice enough because there isn't much more to add than "I agree". If people have variations of the idea, they will generally post it. However, if an idea is bad or generally frowned upon, simply giving it a "dislike" without a reason why or alternative suggestions will not foster a discussion on how to make said bad idea in to a good one. Maybe it IS a good idea, but the suggested implementation is bad and someone else has a better suggestion on how to implement it? Simply giving a "dislike" and moving on lets potentially good ideas just die. It is actually preferred by devs I know that there be a discussion as to WHY something is bad so if a similar idea comes up, they can avoid those points of contention.

2. Some people are just salty. You say something someone doesn't like one time or rubs them the wrong way? You get people who apparently have nothing better to do with their lives than follow that person around the forum and dislike EVERY post they make just for the sake of doing it. If there is a player with a bad reputation who happens to make a legitimately good suggestion or topic of discussion, people will tend to just downvote them in to nothingness without even looking at the thread and that won't get the attention it may deserve. Also "revenge disliking". You dislike someone's idea one time, someone dislikes every single post or idea of yours from now on because you have to stick it back to them but harder to teach them a lesson!

3. "Dislikes" tend to foster toxic behavior. Rather than discussing WHY an idea is bad, the original poster may just get offended and lash out at someone who just disliked without posting. It has happened many times. Granted, people can still post negative stuff about it but with this day and age, most people constantly seek the approval of others on social media. A lot are desperate for "likes" any way they can get it, so "dislikes" tend to foster negativity and, for a lack of a more articulate way to describe it, butthurt.