> Seems like a fairly trivial business expense to me.

Consider a freelancer, relatively new to their chosen profession with a sawtooth cashflow. A one time purchase means they can continue to do their job for as long as the app they bought works on the OS they work on. A subscription service means a bad couple of months and an unexpected bill locks them out of opening any of their old work and limits their ability to do / get new work. Your argument boils down to "well I can afford it, so everyone should be able to"