So a couple of points here:
1.) Apple has a regular cadence and volume to make them THE thing a lot of assembly lines make. The Switch will never do the volume that an iPhone does.
2.) There are *some* iPhones available in the next week. In the case of the 6S Plus and 7 Plus, they took MONTHS to be available on store shelves, especially in the case of the hard-to-produce Jet Black variant.
3.) These factories don't sit idle waiting for another order of Switches to come in. And since Nintendo isn't a high-clout producer, they have to wait in line - any stock that's coming through now was probably part of the originally planned manufacturing run. Increased production would have to bump some other customer ($$$$$$$$$) or be squeezed in via overtime, etc. (also $$$$$). Unless you're Apple/Samsung/et al, you can't ramp production up quickly. I'm not really familiar with the exact timeline, but it's on the order of months, not days or weeks.