Bob has enough assets he can buy an additional rental property each year.

Tim has to save for 10 years in order to get a down payment on a house (and borrow half of it from mom and dad).

Tim rents from Bob.

Tim has to compete with Bob when it comes time to purchase his home.

It is easier for Bob to acquire a house, and during the time Tim has saved, Bob has been able to add 10 homes to his portfolio.

Wealth consolidates more wealth at the top over time. The more consolidated, the more the velocity of consolidation speeds up (The point we are at) via not only how wealth/assets work, but also as Bob has more and more power/influence and the benefit grows of ensuring the system is in his favor he starts to exert more political influence. An orthodontist with two homes isn't bothering with political influence other than zoning around those homes. His son that inherited multiple homes and now rents out 50 is going to every government meeting related to renting in the town, taking the country planner to lunch, knows the council members on a first name basis, and exerts much more political power than his father.