Hello,
PPS pools have higher official fees, but that's not all.
If you try to work for them, you will notice that they tax you in a hidden way too: Your mean hashrate displayed by the pool will be lower than on a non pps pool.
They rarely pay the benefits of the transations.
You usually have 5% of Fee on PPS versus 1%  to 2.5% for non-PPS pools.

On the other hand, you are paid, whether the pool is lucky or not.

This large fee permits to pps pool to have reserves.

The risk for them is a block retention attack by an important thief miner. In addition to the cost of a failure fully supported by the pool, a PPS pool is particularly exposed to this risk