I suppose this can only be answered by the developers themselves but I see no indication that they'll be removing support for any package format in upcoming versions of the OS.
In the past, they've stated:
Because of all of these reasons, we've decided to include support for both Snap and Flatpak out of the box in Zorin OS, in addition to AppImage and traditional .deb packages (using the APT package manager).
[...]
Nevertheless, we believe in the freedom to choose. If you don't wish to use one of these formats in Zorin OS, you can always uninstall Snap by entering this command in the Terminal:
And I agree with that decision, having more choices is better. My only wish is they make Debian packages the default in the software store, instead of Flatpak.
They are Flatpaks (unless they also have snap versions?):
This would certainly free them from the burden of fighting the upstream on every new update. I can say for sure that Debian is rock-solid and has given me no reason to not support this decision.
I guess the reason they're sticking to Ubuntu is to improve hardware compatibility and the continuous update of custom kernel versions. It certainly makes debugging a lot of issues much easier, given how Ubuntu is the most popular distribution and has a lot of people online talking about it, sharing bugs, etc.