I'm not talking about authors, I'm talking about Hive accounts. I agree that witness accounts shouldn't be extracting all they earn too. They do have to cover some expenses, but that's not all they earn.
If there are witnesses profiting from Hive and extracting all rewards, you could withdraw your support.

Do you really think the problem are users than extract 5 or 10 dollars per month?

The power is in the numbers. There are really a lot of accounts extracting. Some of them only extract 5 or 10 dollar a month, some of them extract quite a lot.
That is money that doesn't stay on the chain. If 'we' keep doing this, there is nothing to extract anymore soon. It is already drying up.
It's not that people can't withdraw any rewards every now and then. Only some accounts just withdraw everything. And a few of them don't even interact and just receive (automatic) upvotes because they have been on Hive for a long time and/or have some autovotes.