Are roller bags really an issue if they are still within the dimensions that are allowed? They are great utility wise especially when you're already carrying a backpack. Also please assume good faith, I'm not talking about the people bringing a backpack larger than their carry-on.
Try putting a roller bag in the sizer. It doesn't fit. They are basically never within the size that is allowed.
It's the sizers that aren't accurate. Most roller bags fit in the bins.
Airlines don't enforce the sizer limits, do they? I can't remember the last time I saw this happen.
The sizes are accurate to the rules. Whether something physically fits in the bin on a particular aircraft isn't aligned with the rules.