The reason for compensating miners (with fees, subsidy, or anything at all) is that because in a PoW scheme they provide a service that is vital to the entire market.

In a scheme where solving progressively complex cryptopuzzles does not serve to secure the ledger against doublespends and other shenanigans, mining is, frankly speaking, a waste and should have been replaced with a more reasonable initial wealth distribution routine - of which there are many options (including collusion-proof cryptographic lotteries)

In fact, mining provides outright perverse initial wealth distribution in pure PoS because you are essentially rewarding folks for the investment they have made into another, different crypto-currency scheme (by buying BTC mining equipment), an investment that has been likely already paid off via that other scheme.

That's like if Microsoft started paying me money for the fact that I own Google shares