So you may potentially be setting yourself up for a dead pool if a long dry spell hits.
What am I missing?
That is true for the current proportional method, as well as for solo mining. And if it was not, then the pool operator would take the risk on himself, with such low fees, and then you would definitely be left without a pool..
With proportional you have a 'clean slate' after each round.
With shared MaxPPS you potentially accumulate a big 'debt' across many rounds. Which, of course, would average out eventually, but people may not want to stick around that long.