It is the poor tackle technique they are trying to remove from the game. They want people low and that is why if you start low but the tackled player significantly lowers their height then you will not be getting a Red card. As in the other day can't remember which Prem game but the tackler was 90 degrees at the waist and due to tackled player lowering their height significantly there was significant head contact, outcome rugby incident not card at all, if there had not been players very low then it would have been Red.
How often do we see card for taking he catcher out in the air these days, not often I would say. When first introduced there were lots of cards, people have changed how they jump in the most part. That is what they are trying to achieve in the tackle, hopefully we get there