Because Nintendo
When Nintendo announce a really cool thing, but caveat it with something dumb that nobody understands
"Animal Crossing looks amazing! My kids will love creating their own islands on the Switch!"
"You can only have one island per Switch, regardless of the profile."
"But why?!"

"Because Nintendo."

"Amazing! Mario 64, Sunshine and Galaxy are all coming to the Switch as part of a collection!"

"It's only available until March."

"But why?!"

"Because Nintendo."