There's no property management monopoly.... Not by a long way.
Fundamentally the problem is the company is hired to provide a service for the landlord but that service is paid for by the tenant. Hence usual market incentives for good behavior don't exist.
Lack of incentives for good behavior is the natural outcome of a necessity like housing being privately owned--with no realistic alternatives. Liken this to water; we are free to buy our own expensive water if we want, but wouldn't you be outraged if there were no baseline of free/low cost tap water?
Fundamentally the problem is the company is hired to provide a service for the landlord but that service is paid for by the tenant. Hence usual market incentives for good behavior don't exist.