It must be noted that there are likely silent manjaro users, maybe they aren’t even on the forum, who are happily using their manjaro customized gnome setups with those extensions in question. Can you imagine their response if an update to gnome 40 breaks the setup that manjaro devs provided them with?
Also, doesn’t Manjaro sell preinstalled machines? They can’t have them breaking if they can help it. (I do have some reservations about selling computers to the general public with a rolling distro that actually still requires some maintenance and attention to release announcements, but never mind…)
So while I’ve said before (on the old forum) that it’s better not to hard install extensions in root so users can just add and remove them via browser, I can understand where the devs are coming from.
Disclosure : I’m only using gnome 40 in Anarchy and I’m surprisingly not missing dash to dock too much. Just a little. For manjaro I use xfce/budgie.