re: Why are most leagues PPR?

You could

Or you could use a recognizable system that's been in place for awhile. If you don't care about looking at rankings and data and discussing your league with others based on mutual scoring, then you can do whatever scoring you like.

I can do both leagues. But over the years We have switched out leagues to PPR and auction format even though a lot of people were reluctant. Now everyone loves it. There is no right or wrong, just personal preference.