New users does not get tied to the game due to the auction.
You understand that this site is about BB managing and it is not called eBay. Right?
New users don't understand the clockworks of economics, tactics and training.
They get their new team and they want to improve it ASAP, so they run to the market (if they even consider training, they get the vague idea that it takes a lot of time), start looking for players they like, bid, bid, bid, refresh the page to see if someoneelse is bidding, bid again, etc... Basically the suspence of it all is what is addicting.
If you remove this fun of bidding, you lose the lure of the game.
Now, there is no fact that can prove that new users would always (or most of the time) use auto-bid, but I believe it's very likely.