3 months at that same company did it to me.
For me it was the work culture at the company. Problem wasn't that they expected me to work late nights, weekends and what not. By the way, they did want me to do all that, of course.
The problem, the real problem, was they just didn't get it why I wouldn't want to spend my evenings and nights, and weekends in the office fixing bugs, writing code etc. They really didn't get it. By "they" I mean my colleagues and managers there.
Language barrier was another problem. Your team might have been a bit different on this but in my team it was difficult to communicate in English. And so was outside.
But whatever the communication I could manage, esp. with people outside work, it was really really awesome. But that was too little, too seldom.