To be honest this is quite opposite. When you make 3D game you can re-use a lot of models and art assets from Unity / Unreal stores and easily hide the fact by using some filters or shading configuration.

When you do pixel art you cant just buy bunch of art packs and expect them to work together. And for anything high-quality you'll be creating all the art from scratch for every project.

Of course I not talking about very basic 8-bit stuff, but about something that is actually looks good and well animated.