Not merely a single application, the entire network of Adobe applications, and the interoperability between them, which doesn't just mean still images, but audio and visual effects in commercials, film, video games, physical print, professional photography. Almost any visual media outside of the browser at some point interacts with Adobe and PSD files.

And someone whose employability is probably tied to a specific OS, toolchain or software stack really shouldn't throw stones.

What percentage of professional graphic artists do you think were using non-Adobe products through the early 2000s?

I don't know for sure but I'd wager upwards of 80%.