Who I have the same questioned this topic

Since the iPad's first release in 2010 and continuing into 2018, Manage Verizon Account in cellular settings supported the purchase of prepaid bandwidth even when the iPad had no internet connection.  But at some point in 2018, support for this was withdrawn.  Does anyone know why?

The My Verizon app is no substitute for this, even if it worked on a recent-vintage iPad Pro (which it does not), since it requires an internet connection.

The feature made perfectly good sense for anyone like me who bought prepaid bandwidth on an as-needed basis.  There were some months when wifi was always available, so paying for cellular bandwidth would have been a waste.  In other months, I'd unexpectedly find myself with no wifi connection and no cellular data, but could easily buy more of the latter simply by clicking on Manage Verizon Account -- no internet connection required.

It's obvious that you'll want to buy more of something, whatever it is, when you've run out of it and need it for some purpose.  In the case of Verizon bandwidth, this situation was usefully & efficiently addressed when in the past Manage Verizon Account was working.  But since support was withdrawn for no apparent reason, that's no longer the case.  If I run out of cellular data and have no wifi connection, then I'm out of luck -- frustratingly offline with no recourse.

Does anyone know why support for this eminently useful feature was withdrawn?