A combination of reasons. In the few months that I have been at SO and SE, I have interacted with some amazing individuals right from engineers at Googleplex, California to researchers in UK. I have helped some university students through some really awesome project work, some of which I learnt about even more and followed up outside of the platform of SE as well. I have answered quite a few questions and asked some as well and have got excellent responses. Moreover, the different Se sites that exist have made me enjoy this experience even more.