From the tear downs I’ve seen with wireless charging it’s actually a pretty sizable and complicated addition to just slap into a phone that’s already had it’s space optimized. I’m sure there’s work arounds, but with so many various models and configurations I doubt you could create a one-size-fits all mod that would be popular/easy to implement.
Had to look it up for curiosity’s sake.
While not free, seems to be no overhead for the length of stay on Steam that I can see. Another site includes some more description which might add to the cost though
Regardless, it’s just another unfortunate case of physical copies/backups>subscriptions or “licensing/rent” deals.