Different platforms, the 9x25 Dillon wasn't really invented as a defense or combat type round, it was created so competition shooters who use race guns could wring every last possible drop of performance out of their compensators, 9x25 didn't have a fairly massive gun company throwing its weight behind it. I mean the 9x25 is cool and all, but you need a 10mm platform to use it, and the 10mm platforms tend to be Glock 20s or EAA Witnesses, or 1911s. I know there are a fair number of 20 enthusiasts on Glocktalk who play with the 9x25, but I haven't heard it talked about anywhere else.