Can't really comment on the startup side of things seeing as I'm still in university, but having recently done an internship in a town where I knew no one and going back to school and moving into a place with no roommates for the first time, I've been forced into environments where absolutely no one is encouraging me to go out or meet people or have fun. It's unbelievably easy to stay in and watch Netflix, have a couple beers, and stay inside. Having a large house to myself every single night (after a long bout of having many roommates), I often feel relaxed to be away from everyone, but it can also be very stifling: the silence, the lack of movement, the lack of anything but noise through headphones.
I'm typically very busy during the day, so nightlife is my primary means of social activity. When I show up to parties, it's usually alone, and that's something I've had to adjust to. I go to bars, often alone, and I turn my phone off and strike up conversations. At first, it's incredibly difficult, but over time it becomes more fun. Over the summer, this culminated in my attending multiple music festivals where I spent a majority of the day having a blast in a group of complete strangers, most of whom I will likely never see again. But that's now a shared experience that I never would have just watching Netflix.
One of the most interesting things I've noticed, though, is the reaction others have when I tell them I go to parties or bars by myself (or even to dinner or to movies alone). They're taken aback, and they almost try to marginalize you as some sort of loner. I have plenty of very close friends, and I do my best to spend time with them, but embracing being alone has almost made me less alone in many cases.