Why is Jagex so slow at implementing easy changes/fixes that almost everyone would agree on?

It's not so much about how easy something is but balancing what we are currently working on with a forever rotating roster of player suggestions.

So although something could be relatively 'easy' change, we still need to make sure doing something like that not only goes through some internal discussion but also doesn't affect other projects we are working on.

Hopefully that gives you some extra insight and answers your question.