Why

Hello jorgebest7​ 

I am not sure so I would need video of the illegal pass backs that you are referring to, but if I'm not mistaken the rules were eased up a few years back. It is not uncommon to see defenders intentionally deflect or head the ball to the goalkeeper to relieve pressure, and he/she can legally catch it. From my understanding, as long as the defender doesn't kick the ball, or already have controlled possession with their feet, there would be no offense. Like I said I would need to see your video evidence, but in my experience it is impossible to commit this violation in game, as goalkeepers seem correctly programmed to abide by the rule(s), and the pick up ball function is disabled in user-controlled situations. 

As for the last man back issue, from the screenshot you have shown and other complaints that I have seen, this in my opinion would fall under the double jeopardy portion of the DOGSO (denial of obvious goal scoring opportunity) rules. According to my understanding of this, in a situation where what can be judged as a genuine attempt to play the ball is made, the penalty itself is considered severe enough punishment, and a yellow card is issued instead. If it would have been outside the box, or no attempt to win the ball, so for example in this game an intentional tactical foul, then a red card would have been correct. 

Again, I'm not a referee, so these are just my interpretations, and if someone with more knowledge is here, please correct me. 

All the best to you!