If I remember correctly I only voted once, and that’s it, no more votes for me. How can I earn/gain votes? (talking about feedback.unity3d.com)
You get 10 votes and that’s it. You just have to use those votes very very very carefully.
There is a suggestion on Unity Feedback requesting to allow users to earn more votes: Feedback - 10 Votes per month (+ why current voting system is not ideal)
If you really need to vote more you can create a new account and vote from it. 