>>53376767dude, artists are perfectionist nuts like 70% of the time. Can believe Sugimori had at least an inkling of that in him, especially considering Japan’s work culture.
As for the actual acquiring of art block; by XY, he’d been doing official Pokémon illustrations near-exclusively for at least 17 years straight. Arguably much longer if you factor in RGBY’s dev time and very early concepts. That’s not even including the spin-offs he did art for like PMD (which had his art on both five separate games AND loads of promotional comics). Combine that with old age and probably just plain burnout and it’s easy to see why he started having trouble later on.
It sucks to see him almost completely gone from the series now, but it’s probably for the better. Seeing as his character design has begun to degrade somewhat (see: new anime protags compared to anything he’s done for the main games), it might be for the better.