Why don't they pay for the 500,000 views after the video is re-monitized? This doesn't seem like a hard problem for Youtube to solve.
That risk should feed into how sensitive their automated system is at automatically demonitizing things.
The only way Google cares enough to change this is if their demonetization practices cost them money when they get it wrong.
Does it tho?
Google has the problem of too much advertising space vs too few advertising clients. Being able to significantly cut down the advertising space means they get better prices across the board.
Demonetizing any singular video (especially if suspect or borderline) is one time loss, long time profit.