> Why couldn't they just stay a hobbyist store instead of schlepping cell phones?
Because even before selling cell-phones was a big deal, their main money maker for a decades was being a general consumer electronics store, with the hobbyist thing being secondary at best.
When I worked at a Radio Shack back in 1991 (ish?), I was told by the store manager that they sold things like TVs and Computers for the prestige factor, but that their real profit was highest on the electronic parts.
Because even before selling cell-phones was a big deal, their main money maker for a decades was being a general consumer electronics store, with the hobbyist thing being secondary at best.