Probably because having two separate dependency management solutions can lead to a lot of needless headaches.
And it makes particular sense for Gnome to switch over, since Gnome is focused on user space apps. Flatpaks should generally be more relevant and lower risk, long term, since they don’t require root privileges to install.
But why? It’s job is to install software, why make it worse by supporting less package formats?
Probably because having two separate dependency management solutions can lead to a lot of needless headaches.
And it makes particular sense for Gnome to switch over, since Gnome is focused on user space apps. Flatpaks should generally be more relevant and lower risk, long term, since they don’t require root privileges to install.