With PoW, miners can't really hold on to the coins for very long, so they have to dump it to cover electricity and hardware costs which always creates supply whereas with PoS, a staker can just hold on to the coins they get forever at no cost and their share of the pie keeps getting larger and larger forever.
To be clear, I'm not complaining, if eth decides to pay me 5-10% per year based on my holdings for a simple cryptographic signature, I'm not gonna say no, but it definitely creates a weird dynamic where new entrants will have to buy at the price the stakers decide to sell, which could be sky high since we have no pressure to sell.