I do remember a pinball designer, can't remember who at this point, mention in an interview that Ball Save was introduced on T2 because it apparently was a drain monster. Adding Ball Save would help players feeling less ripped off after a short game. Not sure if this is true, but it is what I heared.
I also recall a seminar from years ago where some industry insiders expressed their feelings about Diamond Plate ruining pinball (no more need to buy a new game as the playfield did not wear out), and Ball Savers as well as they extended the ball time on location, occupying the game longer and making the operator less money.