Because after 10 years they see some rough patches and want to update them, while still using the same core rule and being compatible with all of the 5e books and adventures they have already released. D&D naming conventions have never been consistant for 50 years. What ever name they choose will cause some confusion, because they have never used the same system twice.
Honestly just sticking with 5e is probably going to cause the least amount of confusion of any name they could choose. Calling it 5.5, or 6e, or what ever else they could come up with, would actually cause more confusion and lead people to believe that the old 5e adventures are not compatible with the new version.
Agreed. I would much rather they continue to call it 5E and keep with the backwards compatibility (meaning useability) of the 2014 content. I believe there is clarity in this effort, and it is a worthy effort, as it helps all 3rd parties who have already contributed to the 5E-compatible design environment.
Regarding the position of some who demand that an official naming convention change
must occur, even if it would cause chaos, those positions value personal preferences and proclivities, over the stability of the game. I understand the desire, but I don't value those preferences more than the stability of the 5E Publishing Community.
And separately, for those who want a clean break from Wizards, they can just break themselves free and keep playing a perfectly valid 2014 D&D, Level Up, or ToV, or any other RPG out there that suits their fancy, rather than cause chaos on the way out.
When 2026 comes around, people will still be playing the same adventures from all 5E-clone-compatible releases out there. The D&D 2024 rules will be as compatible as Level Up and ToV, and others. Sure there will be some "Legacy" content, but the game is just growing and being refined, not changed to be unrecognizable. In the long run, I think we'll have a stronger D&D game and strong D&D clones in the industry, each with passionate fans that can borrow ideas from other compatible publishers.
I think this era will one day be the subject of academia and historical debate. Just like every debate that has come before.