A lot of the content wasn't mine because years back, I wasn't really that skilled in model creation and animations soo, here's the reasons

SRB2 maps were used because I wasn't good at map making and Sonic World models and animations were used (with permission) due to lacking modelling skills and such.

6 - 7 years later, I've slightly improved in some areas, like map making kinda. Modelling is still a weak spot for me sadly.

There's also some other stuff I do that gets in the way of my free time for working on games like this one, which is why there's been nothing for years.