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.
This isn't even a legit reason now if it ever was.
Long standing titles ran for hundreds of issues with new generations of readers picking them up and keeping them popular without needing #1's. My first issues of Spiderman were Spectacular 144 and Web of Spiderman 44(which also introduced me to a Gray Hulk??). Same for other titles. Creative teams and EIC's came and went and #1's weren't needed.
If you pick up the new Uncanny they are going to within issues, if not in issue 1 mention what has gotten us to this point. Same for the upcoming Hulk.
It's all marketing to FOOL the stupid that still think #1 means $$$$ down the road. That are they really are saying that today's youth are too stupid to jump in like generations before them were able to do.