For me, it's driven by the perceived threat.
Before the rise of "sudden jihad syndrome" on THIS side of the pond, I mostly pocket carried a 2" Smith 36. That seemed more than enough to deal with a meth head in the parking lot.
But then I started seeing more and more instances of people trying to kill as many random people as possible, and the Chief's Special just started looking inadequate.
I've since switched to either a Glock 19 or a 3 1/2" M1911, either one IWB. I'm still working on a holster for the Citadel 3.5 CS, but have recently bought commercial holsters for both, in case my trial and error holster making continues to drag on.
The threat has changed, and with it my response.