That is something that has bugged me. I have a leak in my car's AC. I have injected the dye, found where the leak is. All I have left is to open the system and replace some old seals, but I can't do that right as the equipment isn't available. So I'm stuck venting to the air as it is the only thing I can do. (I could of course take it in, but some combination of cheap and doing my own maintenance means I don't)

Note that the vacuum pump is often a free rental from the auto parts store, I don't know why they can't/don't rent the recovery equipment.

You're correct, however most aren't going to pay the big cost to do that. A better way is to be able to either borrow a recovery unit or rent it. The other problem is training someone how to use the unit and then know what to do with the freon after recovery. Until it's made cheap and easy to recover, venting will continue to happen.