square please challenge us a little

[Zojha]

If you maintain the status quo, what motivation do people have to improve?

Right now, I know I could Impulse Drive the whole way through Hullbreaker Hard. I'd be bored to tears, but I could do it.

You're kinda answering your own question here.

In general, people improve because getting better at something comes with increased satisfaction or enjoyment, be it via flashier animations, less anxiety about potentially holding people back, a higher engagement level, ego boosts (in the case of PvP), a better integration into a social group or other reasons.
I wager especially the last point is a large reason why the JP community has so much higher clear rates for challenging content (and is probably better on average as well).

Trying to motivate people with frustration instead also motivates them to stop doing the content altogether. So next thing is clamoring for higher rewards to compensate for the frustration caused earlier.