Aside from the technical aspects: Its just my recommendation that a technical discussion (“should we add php 8.2 support for the old product or not?”) should also take into account the possible backlashs on the image of an open source product.
i think the “why” has been asked a few times in Announcement: ownCloud 10 and PHP Versions but only received speculations from other users but no official answer to it. I think that it could be possible that we will never know the “why”.
I have no “big” problem with that decision, as there are save workarounds when you use containered operation models (being it docker or anything else). I understand that the main focus lies on the future product OCIS, but there should also be “sufficient” maintenance for the older one. The switch to a major release of a runtime environment like php 8.x is a trigger for maintenance - at least from my personal point of view ;-).