It's just another sign that the Arthur writers have run out of ideas.

To be honest, Arthur has been re-treading plots for a while now - I recall the "persona swap" being a device used often ("Popular Girls", "Buster's Best Behavior", and to a degree "It's a No Brainer"). One could argue most plot points/devices were used up as early as the 3rd season, though that's out to debate. I suppose when you run a fairly straightforward (and somewhat restricted) show for almost 20 years, these things happen.

When they start making crossover episodes with other TV programs on PBS, then they have run out of ideas.

"Arthur and Barney's Fantastic Fantasy Adventure" - don't even think of funding it!