As far as I understand it, that isn't the case.
It costs everyone something. The pool is a shared reward. So giving to one user reduces what all other users get from the pool. Obviously it's extremely small in the case of one user, but when hundreds of users are piling on the top trending posts they are reducing potential rewards for everyone else.
My vote is reduced in strength the more I use it. So that is another cost.
I could have spent my time finding posts that are new and still have potential to give a curation reward as opposed to an old post that I'm piling on.
If I were to use my upvotes on content and comments, in the way I think we all should, I would have practically no voting power left. There are many users that don't get any recognition because people are concerned about using their upvotes on something that will not give them any reward and will only end up hurting their voting power. Many minnows would love to see more recognition considering they are getting very little in rewards. Not everyone here has dreams of getting rich quick by blogging or will quit their day job etc. We want to have a great environment to see interesting content without the typical trolling and with the potential for being able to make some extra money if people like what we say and do. Therefore giving us the option of a simple pat on the back to more users would go a long way in improving the culture of the community here.
Your upvote is more like your employer paying you, and a thumbs up is more like your employer saying you did a good job today, keep it up. And just like your employer giving you a pat on the back, it isn't as valuable as your wage, but its cost to benefit ratio is very low. It would be easy to add, users on both sides of the interaction would appreciate it and it would have extraneous benefits of reducing clutter in the comment section as users could just click thumbs up instead of posting "Nice post".
What's not to like?
I read your articles on the subject of where the money comes from, by the way. Thanks for taking the time to write it.
Cheers