They have the incentive but they are not configured accordingly. Not all of them. That's why dust/spam/no-fee and "stress test" txs get processed.
Have you used the network lately? No-fee transactions aren't getting included,
and definitely won't be once priority is removed. Dust and spam should not be subjectively determined, fee per kb is all that matters. Miners have a very real incentive to keep their blocks to a reasonable size, it's called orphan risk.
I send a zero fee transaction yesterday. It was included in the first block.
I never pay a fee if I don't have to and still I'm in favor of rising fees, by limiting supply (of space).
Enjoy it while it lasts.