Because why not? It’s recommended in Yarn 2 and I don’t see there being any downsides with Git LFS as the files stores in Git are essentially pointers.
PMs are made for managing and hosting packages, VCS are made for versioning source-code. If you're checking in packages into VC, you're going against the designs of both your PM and VCS. It's a bad idea. Don't.
If you for some reason require redundancy of a package repo, then host your own.