With PoW there's a cost associated with producing a coin with mining equipment and electricity so miners won't sell their coins any cheaper than that which creates a floor price. With PoS there is no cost of production, you just have to own and hold coins which also means that everybody can stake their coins.
Another significant difference is that newly generated PoS coins are going to people who are already holding the coins as a reward. That is generally not true for PoW. And more coins mean inflation so in essence PoS coins are rewarding stakers with free coins at the cost of inflation. Personally it doesn't make sense to me why anyone would invest into PoS coins especially considering the average lifespan of coins and how rapidly things change in crypto - but that's jut me.