Some of this is because young professors try to grade things fairly (such as failing students who never make any effort to learn the material) and get beaten down by the administration because failing students are a lot of extra work for the admins. Then it flows downhill to professors telling the same to TAs.

I remember as a TA I caught a student cheating (very blatant, included a paper trail with obvious lying) and the professor was like "eh, give him an 8/10 instead of a 10/10". That was the attitude 15 years ago, I can't imagine what it's like now if trends have continued..