UngeheuerLich
Legend
As is the case in almost all business/branding/marketing stuff:
Reputation and perception >>>>>>>>>>>>>>> Facts
It doesn't matter that the resulting product is going to almost certainly be the 5.5e (or "5.50" or whatever) that everyone's been expecting for the past 2-3 years. It doesn't matter that all this circumlocution looks horrible and sounds stupid and requires tortured logic.
Preserving the appearance and perception is paramount. Image is everything. Facts are inconvenient weights one must deftly navigate around.
Or. You see it as it is: an upgrade that leaves the core functional and is mostly compatible.
Compared to 3e to 4e and 4e to 5e, the switch is small. In no way warranting calling it a new edition.
It is a half edition though (I count 1e to 2e half edition), going from the playtest. I just think they want to assure everyone, that it is no fundamental* shift in game design.
*I define what I mean with fundamental game design/mechanic:
(Matrix)ThAC0 -> BAB -> half level bonus -> proficiency bonus.