Haven't seen all the specifics but generally it is due to the rimmed case of the 22LR rimfire and wanting to go single stack for reliability. Of course, Taurus found how to make it work with a staggered or doublestack mag, so you'd think Glock could have also done so.
Hell, Keltec managed a quad stack with the CP33, so no real excuse there (other than they don't want to have to make more than one model of mag for ban states).