You don’t need price fixing for any industry to go this direction. Take the gas station idea. You’ve got a corner with 4 gas stations. Each one can see the traffic the other ones get and can easily see how much they charge. All it takes is them saying “well, people are still buying gas at that station for $X more than mine, so I’ll charge that as well. And soon they’re all skyrocketing to whatever the consumers can afford.

Calling a group put on Price Fixing requires proving they colluded together to do so, but that’s not required in this scenario. Every landlord can see how much other rents are and if they can make more money and keep their renters or get new ones, they will push that limit. And honestly if they can raise it enough to cover some vacancies they’ll do that, charging 30% more but having 10% empty is still a net 20% in their pockets.