Rental companies buy their own fleet and they get leases from the manufacturers. When it comes to purchasing their own fleet, they'll likely buy as close to base as possible to keep the initial cost and depreciation costs down. Most fleets are purchased this way; think of how often you see a company branded car with steel wheels. The manufacturer that provides the leased vehicles determines what trim level to send, given that they'll be receiving them back within a certain period of time/miles. Higher trim cars are typically the first ones produced when a new model comes out, and they're easier to resell as a CPO vehicle, hence why the manufacturer will prefer to provide these on lease.