Being able to teach is very different from the troubles of grading. I do enjoy teaching. But grading is draining and extremely time consuming. The only way it isn't extremely time consuming is to do it in a half assed manner. Which is why that is likely so common. Honestly, being inside academia I think one of the big reasons for grade inflation is simply because the effort it takes to grade seriously (and other academic politics that couple with this create bad incentive structures where you aren't focused on teaching nor on research).