I'm nostalgic and loyal and those are dangerous things when mixed together. The combo of both along with where I fly internationally has me pretty much a Delta or ST only guy.
As for nostalgia and loyalty...my late grandfather and late father both had long and distinguished careers with Delta. My mother's pension is tied to my father's survivor benefits. Heck, I still have a pass card with Delta though I rarely use it. My grandfather was part of the design team that created the widgit way back when. It's in my blood. I love to fly Delta jets, they're ready when I am, and it shows!
I also fly regularly to SVO and LED and places beyond PEE (I love that one), OVB, BAX, and TOF. Only one major alliance has any reach into 3 of those last 4 places and that is ST. The non stop ATL to SVO flight is a God send for me. The Elite Plus status makes SVO1 bearable and FF miles are best spent securing seats up front on one of SU's new Airbus or Boeing aircrafts for the red eye flights to Siberia.
Take away Aeroflot from ST and the non stop from ATL to SVO and I probably still fly Delta though. After all...I am nostaglic and loyal and those are dangerous things when mixed together.