Back in the 1970s, ActiVision sued Atari for the right to be a publisher but not a platform. The idea of being a publisher but not a platform was a new idea at the time.

But most gaming companies aren't, and have never been, platforms. The exceptions are Atari, Mattel, Commodore, Nintendo, Sega, SNK, Hudson Soft, Sony, Microsoft, Steam, and CD Projekt.