Those repackages of libreoffice packages are actually official.
https://www.libreoffice.org/download/libreoffice-from-microsoft-and-mac-app-stores/
These versions are free software (as in open source) but there's a small charge to cover the effort of putting software in the app stores, and to help develop the software (and build our communities).
What's a natural monopoly? Valve currently has the freedom to implement anything they want within an extent because they're so popular. If they decided they wanted to charge devs 35% would people stop using it? Probably not. Steam's monopoly is as bad as any other for the same reason any other monopoly is bad.