I mostly agree with you, Cailin, as someone who has also moved around a lot on different continents, and whose close friends, as a result, are scattered between São Paulo and Switzerland.
I'm a writer with a small child living in rural England (am not originally from the UK) and despite all my efforts, I find myself lonely where I am. It's no one's fault. I have joined things, gone to toddler groups, accepted all invitations, issued invitations etc, but the fact is that I am not a good fit with the people I have met in this village and its surroundings.
They are mostly SAHMs of small children, whose families have lived in the vicinity for generations and who have no plans to leave, and theyhave been very nice, but clearly regard me as rather an odd creature - foreigner, writer, no ties to the village, renting, will probably move on in time, no fund of village gossip, only one child, strange interests, etc etc. I've never got past the initial chit chat stage with anyone, in over a year and a half.
But, as I say, it's no one's fault. I've tried, and people have been welcoming, we just speak different languages, and I am viewed as liable to move on in the near future, so my child won't in fact be in little X's visas at the village school, so I'm nit quite 'real' in the way other people here are.