This has probably been said ad nauseum in here but Wayne still showed a little bit of creativity, depth, and diversity to his bars on C3. By C4 era every track was one long punchline verse and it was effectively what people could point to to say "he fell off".
Wayne is one of the rare guys that's changed his style a good 2 or 3 times, and C3 was the culmination of his commercial success but also the end of his major comeup.
What probably happened is he felt like his commercial success came because he started being out there and imaginative, rode with that but now the wheels fell off that wagon and he's too big to care.
Once an imaginative/witty rapper falls out of that "zone" (ala Cam/50) they risk becoming boring caricatures. I can't think of a mixtapes worth of Wayne material since 2009 that could compare to the Dedication 2 or even the Drought 3 which is kind of overrated because of it's highlights