The thing with upvotes is that there is also a Voting Power percentage. Every time you upvote something, that percentage gets a little smaller. The smaller your VP percentage is, the less your vote is worth.

Were I to upvote with full VP percentage, I'd give 0.02/0.03 reward. Do I upvote with 50%, I'd give 0.01/0.02 reward.

This percentage regenerates with time, but this is why we don't just upvote every single post out there.

I hope this explanation helps!