The engineering problem for smoke alarm batteries is very different than the one for a PLB. A PLB requires much more power and is subject to wildly different environmental factors in terms of temperature, pressure, water, dust, shock, and movement. A smoke alarm has a test mode that does not activate a worldwide rescue system. A PLB would probably have to be a lot bigger to hold enough AA batteries to reliably have enough power compared to the batteries they use today.

I am not saying it could not be done, especially with CR123A lithium primaries and a different form factor, but it is not the same engineering problem as a smoke detector.