This site is about what happens on Stack Exchange. Per the help centre
Meta Stack Exchange (MSE) is the primary feedback and discussion space for issues that relate to the sites on the Stack Exchange Network and the software that powers this platform.
Why is wikipedia asking for donations is about Wikipedia, not about Stack Exchange at all so it's not something you can ask about here. The closure message told you that.
Platinum badges, however are on topic. The problem with that question is that it's already been suggested.
- So you're lacking research because you've not looked into whether it's been suggested before, or if you did you didn't say why your question provides a new slant on the topic or why users that have been here a long time need to be further motivated by extra badges
- and this being Meta it's quite possible people simply think that platinum badges aren't a good idea and voted accordingly.
So make sure your questions are about Stack Exchange and try to see if something similar has been asked before and what reception it received when it was asked. If you are going to repeat what's been asked before then you need to offer some new insight into the problem.
Finally start from thinking about why something is a problem and then how to solve it rather than thinking of a feature (e.g. platinum badges) and then wondering how to justify wanting it.