Because 1. It counts as engaging with the post which is not the intent ( I almost never give a negative reaction. If I don't like something I just ignore it ) 2. There are clients that show the List of Likes/Reactions and these posts pop-up if Mute Lists are not used & pollute that page. And like you yourself mentioned, what counts as a positive & negative reaction itself is a flexible contextual thing...eg.I use 😱 emoji, mostly as a faux-shock & never negatively. So I am not sure it's useful to add reaction of any sort, especially if I can't undo it. Would appreciate if you could reconsider.

It doesn't count as encouraging. Reactions can be positive or negative. There are plenty of reactions ( 👎😡🤬😰😓👇⬇️) being used daily to demonstrate discontent with posts and people definitely don't want to see them in their profiles. Whoever is encouraging everything you react to needs to fix their client to filter the negative stuff out.