Because he's still the fundamentally same guy at the end, and any information he learned surviving in the wilderness and fucking with Monks wouldn't really be applicable to the school grind that compromises pretty much every S2B episode past RwS. I doubt he learned about Math and Earth History, for example.
Because he never really got to fuck with grills with the Monks or in the wilderness, he still has no idea what to do, although keeping his time with Jackie and Star intentionally apart prior to Just Friends was a great idea overall, even if he did it for the wrong reason.
And any further corruption from either the Arm or whatever was up with Eclipsa's chapter would probably require a magical trigger, since they were mostly "cured" as of right now. The symptoms are gone, but it's still there.