You can only see it as a “move” if you consider Debian to be a single reasoning entity. But consider: the person making such a patchset would be the Gnome maintainers, and they would not really have an incentive to do so; Gnome upstream probably changed the default for a reason, and the maintainers of the Debian Gnome package, being voluntary maintainers, probably are philosophically aligned with Gnome upstream. The rest of Debian, like the package maintainer who chooses what Desktop Environment should be the default, can not make such a change to the Gnome package without a quite adversarial process involving the Technical Committee, and in practice this process is rarely used, and even when used, rarely successful.

Therefore, it is the expected result that Debian should follow the upstream Gnome into using Wayland.