"Greater responsibility for contact"

[Kansas Ref]

Similar to the dribbler having the "greater responsibility for avoiding contact", this is also seen in other cases: 1) A1 receives a pass in the high post and B1 has obtained LGP (legal guarding position); then A1 proceeds to bull-drive his/her way thru the lane and trips over the leg or foot of B1 and falls down hard on the floor (mind you that B1's foot was already there first). Or 2) A2 is driving thru the lane from the perimeter, with B2 having obtained LGP, then A2 trips over the foot of B2, falls down hard on the floor.
I have frequently observed where officials (NF, NCAA, NBA, IABBO, etc.) will call a "block" on B1 [or B2]--despite B1/B2 having his/her foot on the spot before A1 decided to mush their way thru. In this case, really A1 / A2 has the "burden of avoiding the contact"; however, presumably due to habits and expectations, B1/B2 is always called for the foul.
I officiated a game recently wherein this case presented itself to me early in the game. A1 dribble driving through the lane and simply tripping over the "already set" foot of defender. I did not "whistle" the play and the coach was aghast saying "look at my player limping cause he got tripped up". The coachcalls a time out and comes over to ask me: "hey didn't you see that?!" to which I replied "yes, I saw your player trip over a defender in LGP".