1) Why pay when there is a option for FREE?
Not really free! By mining this transaction, since the space is limited, we are not mining other transaction(s) that would increase the reward (opportunity cost). Thus is the same thing to pay the fees first and then "get them back" on the next block. Same for pool and miners, but miners get the reward earlier!
The ones effectively 'pushed off the bottom of the list' are the lower fee transactions i.e. they are not worth much or even could be zero fee transactions.
Pool fees here are low, if you think they are too high, then by all means, mine somewhere with lower fees, that also pays txn fees to the miners, i.e. above PPS
