>>546374519
It's a pretty easy explanation.
>90s Sonic fans whined about the 2000s being too anime, serious, and having too many modern characters
>Sega complied, scrubbing all this with Unleashed as a beta test but fully went with it starting with Sonic 4: Episode One
>The series was also selling extremely well on Nintendo consoles and it's known for having a large children fanbase, so might as well pander to them as well
There was also a major cultural shift when the 2010s happened. People were tired of dark, serious stories with tragic protagonists and complex artstyles. They wanted something more lighthearted, wacky characters, and softer artstyles with the storytelling being more subtle with it's serious themes.
I'm not sure if the Sonic series could survive the 2010s culture without being affected by it, if SEGA ignored their millennial fanbase.