The thing is that if a truly neutral judge (ie. many Utd fans are biased towards us while many rival fans are biased against us) went over our penalties last season, it's fairly obvious that we were wrongly given two penalties. James against Norwich and Bruno against Villa, both of which are absolutely fine to complain about. But all our other penalties were fine. We also had one absolutely blatant penalty not given our way (Fred against City where he was ridiculously given a yellow card for diving when there was big contact) so we were the grand total of +1 over the course of the season. Hardly enough to warrant the ridiculous amount of attention that it has received. And that's not even including quite a few others that probably 'should' have been given but I'm not going to include them as they weren't 100% guaranteed.
Just in the most recent game there was another incident that we probably should got another penalty and the opposition player sent off when he went in elbow first and got Pogba in the face while being nowhere near the ball. Yet all the attention seems to be on the penalty we later won that was quite obviously correct. Makes me wonder if anyone complaining about it has ever played physical sport before. The contact the defender made on him is literally a tackling technique in rugby league and union called an ankle tap - when an opposition player is running away from you you tap their back leg over so it hits their other leg and trips them over. Yet according to these 'experts' it was nothing and Pogba dived.
The defender didn't mean to make that contact but that doesn't mean anything, knocking over a player accidently through clumsiness is just as much of a foul as doing it deliberately.
You say it's not because we dribble in the penalty area more, but that almost certainly is related. Both Martial and Rashford in particular (Pogba also does it when he gets in the area ) are often guilty of overplaying when they get in the box. They get the opportunity to shoot but instead of going for it they'll try to go past another player or two to create a perfect opportunity. Sometimes it works and they do create a better chance. Sometimes (far too often) it gives the defender the opportunity to actually win the ball and the chance is gone. And sometimes it wins a penalty as a defender tries an all-or-nothing tackle that doesn't quite come off. Quite likely we'd actually score more goals overall if they'd just shoot the first time instead of trying to do do more, but it is what it is.
I don't watch enough of Liverpool, City or any other team to know whether they should be getting more penalties. Maybe the reason we got so many more penalties last season is because all these other teams were getting screwed over with the referee decisions. If that is the case then by all means complain about that. What I do know though is that complaining about the number of penalties we've gotten is ridiculous since we really only get the penalties that we should be getting.