Why does Apple need to provide the plan as well? I mean, given Apple's controlling nature, they may well wish to - but most laptops with mobile internet simply

Why does Apple need to provide the plan as well? I mean, given Apple's controlling nature, they may well wish to - but most laptops with mobile internet simply provide a SIM slot hooked up to a standard mobile baseband. Customers find their own plan, and many carriers offer plans which are tablet-oriented, with no calls/texts and sharing the data from a 'master' mobile plan.