When the new out of bounds stalling rules first came out (2014-2015), pushing someone off the mat was also supposed to be considered stalling. Here's the press release from those rule changes. IMO, they didn't want people to win matches via push outs. They called it that way occasionally the first couple years, but rarely call stalling on the pusher now. Thus, it's even more of a strategy to simply shove the other guy OB and get a stall call.
From the article linked above, the possible calls when wrestlers go OB are:
"1. Stalling on one or both wrestlers for leaving the wrestling area.
2. Stalling for pushing or pulling the opponent out of bounds.
3. Wrestling action is taking place. (It should be noted that a tie-up, including an under hook with no attempt to initiate an offensive move, is not considered an offensive or defensive attack)."