i think its a default position that people take, because they don't want to use an outside based offence, and have not experimented with II or OO and obviously don't want to use Princeton.
thus this leaves them with BO, Patient, or PTB
PTB tends to highlight some stamina issues, so people play safe and go BO.
That's what I used to do anyways. had a fair bit of success with OI recently. Probably be giving II a go during my Private League games, see what benefits I get out of that.