Why people repeatedly trying to sniff GSM with varies devices? from a RTL-SDR to real SDRs, point has been proven for many many times, GSM encryption is broken since a long time ago.
This is specifically my point of view, but I'd be willing to bet people keep doing this because they are curious, to see if they can or just because they want to expand their technical abilities.
Right, "it's been done" is different from "I did that"
Also, repeatability is important