incentives to earn are obvious. but what is the incentive to upvote various things?
posts
upvoting posts will make the post more visible to others. so you would upvote a post if you want to promote something.
how often do you want to promote something?
comments
i could see myself mainly upvoting comments that are unpopular, but that i agree with. this is basically a way to flex an opinion on the site and make your position known / more acceptable.
general upvoting
upvoting content that you like would theoretically help to tailor this website to have more content that you personally like. so by upvoting content, you're increasing the enjoyment that you get out of the app
idea
upvotes naturally have a positive moderation quality. so you want your users to upvote good content. but the main person benefitting from this positive moderation is the owner of this website.
what if there was some kind of system where if you upvote something and a lot of others also interact with it, then you get some kind of kickback? it would be sort of like investing in content and seeing a return on it. maybe too complex though.