> If "just hotspot your phone" was hunky dory why does Apple sell iPads with cellular modems?

Because iPads are fundamentally different than laptops. Workers use tablets in the field all the time, often for shorter, quick, one-off checks and such. If you're in a fleet truck or on a job site, having a tablet on the passenger seat to check on work orders is easy. Pulling out a laptop is a much bigger pull, and more awkward.