I can't mount Zeno Clash into Gmod, what gives?

I recently got Zeno Clash especially so that I can mount it into Gmod, yet inside Gmod it reports as unavailable even though Zeno Clash is installed and verified on steam…
Why does Zeno Clash mounting support option still exist inside Gmod if it doesn’t work?
This is retarded…

Try installing the Zeno Clash Models in Tools

If that doesn’t work, then it’s because the game hasn’t been steampiped.

The game had been steampiped. You just need to get the models tool.