And why not use PC-derived hardware. Developing a custom chip is expensive and games can't be ported from PC<->consoles easily when it's not the same chip. Also, when producing the same chip, the price goes down for everyone when more of it are made (economy of scale).
Valve co-founder Gabe Newell's decade-old claim that consoles have shifted from bespoke graphics designs to PC-derived hardware has largely been validated, with modern systems relying on x86 architectures and AMD-based GPUs alongside PC-like features such as upscaling. As Valve and Microsoft move toward PC–console hybrids—via a new Steam Machine iteration and the rumored "Project Helix"—the divide between console and PC ecosystems continues to narrow, emphasizing shared hardware foundations and cross-library play.