They probably don’t care if you use a different service if you don’t log in to use theirs. If you don’t log in they can’t easily monetize you by tracking your data and building a portfolio. Otherwise you use their resources at a cost and they don’t make money.
So threatening to leave for other services isn’t exactly a threat.
Are there any studies that link phone use inside schools to those issues? Because I can easily believe that declining grades could be attributed towards the use of tablets and laptops being used in classrooms as well which many schools are encouraging or increasing the use of.
As for attention spans I would believe it’s for the use of phones/tablets/electronics from a young age rather than the use of them inside of a school itself.