Several curators spend several hours every single day trying to find the best quality posts and they'll stop doing so and switch to casual mode without an incentive.

Most of the voting is done by people without an incentive because they get near to zero rewards for it anyway. Many people pick up good authors and resteem them to give them exposure, without a financial benefit.

I think people vote because they like the content, and they will continue doing so without financial incentives. Perhaps the ones that vote for incentives/rewards can be missed.

There are very few independent voters with big wallets, I wonder what somebody like @blocktrades would do if there were no curation rewards. Maybe he and his better half would merrily curate along, in the interest of the platform and the price of Steemit.