Each time a post gets paid much of it is paid to the curators, mainly those who voted for a soon-to-be popular post early on, identifying quality content for the community. This is a valuable service and is thusly paid.
But does this really incentivise voting for content that you subjectively judge is of high quality?
I'd very much prefer to simply vote on the posts that I like (like any other social platform), supporting those who made the content, encouraging them to produce more content I like. A wonderful cycle. But I'm economically disincentivised to do such. Instead, I must vote for the posts that I judge most people like, even if I personally don't like the post. It's too overly complicated.
Sure, some people will ignore this and altruistically vote on content they like, even if it earns them less. But the more steem power you have, the more you lose from altruistically voting, especially since voting power is proportional to your steem power squared. As a result the votes that matter the most are hugely incentivised to only vote strategically.
Stomping on diverse content
This manner of rewards also effectively discourages the production of diverse content. Say I'm a fan of chinese novels and someone makes a very high quality post on the subject. Now most people aren't interested in chinese novels, so it's natural that posting about chinese novels shouldn't earn you much right. But if everyone is strategically voting, posts on any topic that isn't mainstream won't just earn less, they'll earn absolutely nothing.
Right now I think Steem is too small to suffer much from this particular effect because it doesn't have much diverse content to begin with, but it is a serious issue that will become larger and larger as Steem tries to grow.
War of the bots
Then there is the resulting war of the bots. It has been mentioned in several other posts such as this one, and that is that the voting competition is already causing the development of intelligent voting bots that will continually get more and more advanced over time. Who would want to join a social platform ruled by bots?
The 30 minute rule has been put in place in an attempt to stifle bots. Voting less than 30 minutes after the release of a post will cause the rewards to largely go to the creator and not the curator. The idea is that bots competing to vote as early as possible with each other will destroy all margin of profit in the process. Maybe this will stifle the bots, but I don't see it eliminating them, just requiring the bots to be smarter and lowering the rewards for botting.
In the meantime voting for the averageman has become all the more complicated. What's the point of the new feed of posts when it's worthless to vote on new posts? You find a post that you like early, but once again instead of just voting on a post that you like, you must now also enter the artificial game of deciding when to vote on it.
Alternatives
There's 2 alternatives that I can think of.
The first is no curation reward at all. Now, why would anyone vote if there's no monetary reward for doing it you say? Well same reason people upvote stuff on any other platform like youtube or reddit. Because you like the content. It eliminates all the problems mentioned above. There might be less voting going on in total, but it would be of higher quality.
The second is there's still a curation reward, but the reward isn't affected by the popularity of a post in any way. Still eliminates the problems mentioned above, but you still get rewarded for voting.