It was mentioned briefly, but there are many things only something like a high end gaming PC or workstation can do. 3D modeling (Architecture, Machining, Game development, CGI Animation, Electronics design, etc) Running virtual machines, databases, running servers and test environments. Deep Learning, AI. Now these days there are alternative online cloud solutions for a lot of this, however, for many people there is still value in doing it all in house.
#1 for me would be the games I want aren't available for consoles. I'm an old school PC gamer, a lot of the long lived titles are still on the PC only. Though with remakes here and there they are starting to fill in.
Not very many Real Time Strategy titles make it to console for example. High end Simulators. (Honestly not much reason either, the right peripherals and the consoles would be just fine for a lot of PC titles)
Can't really get a gaming GPU at reasonable prices either, unless you are lucky.