Uncanny X-Men has a new number one because of both marketing and STORY purposes let's not forget that. Sales is a primary reason but they restart the book at one because it is now Cyclops book.
I'd argue that the story reason came from the sales reason. They wanted to reboot Uncanny X-Men so they created Schism to come back with several new number 1s (is it just Uncanny and Wolvie?). X-Men has gone through multiple changes of direction without relaunching. While there was a name change, Morrison took over at issue 114, which was the biggest change the X-Men have ever gone under. And then when that ended, the change started at issue 444 of Uncanny X-Men at 157 or so of X-Men. Then when they went to Utopia, none of the numbers changed either.
So yeah, you have to look at sales when it comes to this. Everything else is a very distant secondary.
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