Uninstalling a package manager through apt won't uninstall everything that package manager installed during the time you used it.

If you want to fully delete Steam after uninstalling the steam package, you can delete the ~/.steam and ~/.local/share/Steam folders.

That won't delete everything, though, because each game can store its files wherever it wants. Some games store files in xdg locations like ~/.cache, ~/.config, and ~/.local/share, but others store files in your home directory or elsewhere.