Because now that this is a 3D game that'll take a lot more effort to make, the dev wants to earn money off it. Issue is, you can't really make money off copyrighted characters unless you want a DMCA from Sega.
Sadly, a 3D game takes a lot more time and effort to make than a 2D one, and I imagine the devs' Patreon is how they're going to afford not just living, but also commissioning assets for the game.
