Because Amiga needs one unified direction to move forward, not half a dozen different variations that are all doing thier own thing.
As I said already, in previous times I thought the same. pOS? No, no split! Etc. Hey, even when they wanted to create a MorphOS-Newsgroup, I voted - as still is documented - AGAINST it. Just no further splitting...!
But much time has passed. Products came from Genesi, lies from Amiga Inc. And especially incompetence in that very one important function the respective owner of the Amiga trademark has to fulfill: leadership. The ability to lead the projects, the development and the users of the Amiga market.
So in my opinion Amiga Inc. lost any right to claim their way as the only one.
Okay, finally - veeery late - they reconsidered regarding the option of a PPC-AmigaOS (instead of DE only), and again much time later they gave the project into the hands of people who seem to be able to finally create an OS4.
BUT, and that is the second point, in the meantime - while of OS4 currently just the kernel is running on the AmigaOne -, there already is a product purchaseable that could, from the look&feel etc., as well be called "AmigaOS4".
Therefore - all the lost time in all the years since Commodore's bankruptcy and AI's many changes in direction in the past, etc. - and because we all do know how much could happen suddenly until OS4 really would be released (Who doubted Gateway would bring us a new, modern AmigaOS, for example?), some people, like me, prefer today, in 2002, to choose that option that's actually here and represents all we ever wanted.