I'm not sure why is it condescending. I have met people who do this all the time while I'm trying to just have a drink/dinner or get to know a person, but I'm just not able to connect with heavy instagram/facebook users. I prefer not to see them again, as for me it's very boring, and I see them as being unkind, when in all fairness they are probably just social network addicts.

It's condescending because you're focusing on the media that people use rather than what they have to say in life. There are (obviously) millions of interesting, passionate, intelligent, creative people using both of these apps.