This works both ways because legitimate software developers also don't have easy ways of pushing their signed software to end users. Usually step 1 in installing software from external developer is "get my PGP key imported" [0].
[0]: https://www.sublimemerge.com/docs/linux_repositories
I don't mean Linux distro's model is worse or that Windows model is better. What I mean is that none of them is significantly better than the other. Just different with different trade-offs.