But why not though

I also use tailwindcss in a non-node project, but use npm package / lock files to easily lock javascript / css dependencies and make renovate able to update them for me.

I've linked to why. We prefer #NoBuild solutions where we'd only use local npm deps/node_modules if we absolutely have to, and for non JS Apps we don't.

The node_modules folder is still somewhere on your system (~/.npm/_npx probably?) containing the same tailwindcss dependency files, but if it helps you sleep easier at night it’s okay to pretend it doesn’t exist.

No kidding, I thought global tools worked with fairy cloud dust, now I wont be able to sleep! But knowing there's not a going to be a bloated node_modules folder and local dependencies running different versions unnecessarily maintained in every project will definitely help.