I think one of the reasons that one is not used because usages like "Simultaneous Location And Mapping" (instead of the "Simultaneous Localization And Mapping"

I think one of the reasons that one is not used because usages like "Simultaneous Location And Mapping" (instead of the "Simultaneous Localization And Mapping" that SLAM stands for) would read a bit strange... "location" is more commonly used to mean "the place" and not "the act of finding the place".