Just to give some support to your point. I am a casual player who played in the last season. The reason this happens with casual players is because of how the rifts ramp up in difficulty, and the gear breaks that you get. From 30-40, you are grinding for set items. Then, you finally cap off your build. And you jump up to 45-50 fairly quickly after that. Then, from 50-60, its a bit of a grind. Finally, once you hit 60+, the grind gets more and more intense.

For a casual player, those quick jumps stand out a lot more. You feel awesome playing because you are crushing level 45-55 rifts. You feel invincible. Then, that all comes to a halt. And they don't understand why. It is because from there on out, you are grinding for gear with specific stats, in ancient forms. And you are grinding paragon. That is how you get out of this section of the GR's. It definitely shifts gears once you get into this level of rifts, and more casual players don't understand what that shift entails.