That was the initial plan but it hit a number of roadblocks.

1. The release of the Robotaxi product was much delayed, and had Tesla kept to the "no buyout of leased cars" they would have been swimming in returned vehicles with nothing to do with them yet.

2. The policy was put in place at a time when the autonomous hardware was thought to be the "final" version (referred to as Hardware 3). It turns out the "final" version wasn't powerful enough, so a new final version was released (Hardware 4). So all the cars that were leased were not going to be useful as taxi cabs, so they offered those for sale to their leasers.