bang, I think it's that people get *lonely*. It's all well and good to study French and piano. I'm not deriding those things. Certainly do them if they bring you joy. But I think outside of major cosmopolitan cities (like Bangkok, Shanghai, etc), it's much harder to meet and connect with people and, by and large, people are social creatures to varying extents.
The issue that *can* arise with trailing spouses is that, yes, they can study a language or read books, but that can only take you so far. People want to meet people, have friends to chat with, go out with, discuss books and language with. And outside major cities, this can get appreciably difficult. I'm in a pretty large city myself, but it's no Beijing or Shanghai, and I often see trailing spouse wives very active at my school because they don't have a lot of other social connections.
Advice: Teachers with dependents
Like I said before, my wife is coping here, but it's difficult because we're not in a cosmopolitan city. She does various things (besides facebook) - cross stitch, shopping, gym, exploring various parts of the city (which aren't much), learning to cook, studying advanced English...but it's not easy, especially because we don't have many friends here. She was going to join an advanced English class to improve her writing but the school was charging wayyyy too much and she really didn't like the idea of being in a class full of Chinese people (she's Thai). We have one more year here and that's it - either we move to a cosmopolitan city or we go to America. And after reading some of the comments here, the latter is looking like a better option.
When you are a native speaker of the language, there is nothing to 'learn'.
And people's interests are different, so while your interests make being a trailing spouse a great life, it is not for everyone. Even in big cosmopolitan cities. I know plenty of colleagues that never bother learning the local language, eat local food, participate in local activities etc etc. But that is their choice. Expecting other people to enjoy what you do is unrealistic and it's annoying for them when people force things on them.
And people's interests are different, so while your interests make being a trailing spouse a great life, it is not for everyone. Even in big cosmopolitan cities. I know plenty of colleagues that never bother learning the local language, eat local food, participate in local activities etc etc. But that is their choice. Expecting other people to enjoy what you do is unrealistic and it's annoying for them when people force things on them.