Why are frontend frameworks in NPM?

When I’m looking at some github projects and tutorials I look at the package.json file and see frontend frameworks listed as the dependencies quite a lot. I don’t get it. I thought Node was backend? My understanding is that to install frontend frameworks you dl them directly from their website or github or use a CDN then link them in your pages - all this has nothing to do with Node.

Even if I did install a framework through Node doesn’t it save it to the node_modules folder? There must be a reason for it as I’ve seen a lot of projects list them in their package.json file. Can anyone explain this to me?