Lack of integrity.
Saw a clip of a game from many years ago. Vinny Jones absolutely poleaxed Steve McMahon with a very meaty challenge. McMahon simply got up and kept playing. It was a late tackle and a foul, perhaps a yellow (I think Jones escaped a yellow) bu there was no yelling in faux agony, no rolling over holding the face, not gesturing to the ref. McMahon just got on with it. Nowadays players are waitng for contact and sometimes seeking it out so they can cry out and roll about a bit to gain an advantage. I am all about protecting skilled players from hod-carriers deliberately beasting them but I lose sympathy when the purposely look for contact so they can con the ref.