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)...