Because we feel that Qolsys is currently the best experience with an Alarm.com compatible alarm panel, with the easiest programming, the most rapid development, the widest and most secure set of available sensors, and access to features no other panels in the ecosystem offer. Here’s another description of the difference.
Conversely 2GIG has left some frustrating and questionable bugs present in the GC3, which despite 2 years of numerous and frequent reports and complaints from multiple dealers, have gone unresolved through 4 subsequent firmware releases.
The GC2 and GC3 are still solid platforms, but development has slowed and the panels were replaced by the GC2e and GC3e. These encrypted models improve security by using encrypted sensors, but the GC3e still has the same fundamental firmware problems because it shares firmware with the regular GC3.