They can only do that for the packages they build themselves, which are mainly useful to enterprise customers.
Qt being under LGPL, there is nothing that prevents anyone else from redistributing open-source builds of Qt - Debian / Ubuntu through apt, MSYS2 (pacman -S mingw-w64-qt5-whatever), homebrew (brew install qt), conan (conan install qt/5.14.0@bincrafters/stable), vcpkg (vcpkg install qt5)...
Sure. But 99% of people use those packages. Not sure why you say they're only useful for enterprise customers, as they're literally the reference packages. :)
On Linux/BSD though, obviously most people use the in-built package managers where the Qt version is recent enough for their purposes.
Qt being under LGPL, there is nothing that prevents anyone else from redistributing open-source builds of Qt - Debian / Ubuntu through apt, MSYS2 (pacman -S mingw-w64-qt5-whatever), homebrew (brew install qt), conan (conan install qt/5.14.0@bincrafters/stable), vcpkg (vcpkg install qt5)...