Generally it is done with a team's trainees who only play in scrimmages or in garbage time situations. I don't do it so I am not the best person to explain it, really. I think that a lot of the people who were/are good at it buy free agents- very good players saved from teams that have gone bot- at reduced prices then turn around and sell them for market value. Check out the transfer history of most of the teams in the BBB to see how it worked/works.
Once I scored a basket that still makes me laugh.