from years of lurking here, it seems that there are a few categories of people who would say 'i'll never move back'
those who say it the most emphatically are the ones who have left bad situations behind in the US. a fair amount of people on here seem to have have had serious financial issues in the US, and i think appreciate the government safety net in the UK more as such.
another handful have left very difficult family relations in the US, and are more comfortable with the distance.
others have moved here to be with a partner or spouse, and have naturally fit in.
how one does or doesn't settle in the UK is not something to be proud or ashamed of, though you will find that attitude in some posts. everyone is different and has their own place in the world.... people on both sides of the pond wear rose colored glasses from time to time, so don't worry that you are missing something 
I think this is a good post. It is true that some people are very proud of the way they have fit in here and tend to be a bit critical of others who they feel "aren't trying hard enough" or what have you. But everyone is different, and you are right, there is no reason to feel ashamed about not fitting in as well as other people have or being more homesick than some other people. I struggled during my driving lessons a bit, and a lot of other people just took to driving here straightaway, which made me feel a bit embarrassed, but really, it isn't down to ability (all of those people and myself included were confident drivers in the states and probably on a similar driving skill level) but it often comes down to confidence and belief in yourself. Some people have it in abundance, others have more anxious natures or a lot of self-doubt (like myself at times). And there are those of us who were a bit lonely in the US, or didn't have health insurance or had financial difficulties, or who aren't too close to our families, so I think all of those statements are pretty fair, though it isn't the case for all of us, of course. So, to the OP, you will always get different responses from each person to questions like this, which is what makes this forum so great.
But for my personal reasons, I think the following are pretty big perks of living in the UK:
1. My family - yeah, pretty obvious, but it's true. My hubster is my best friend, and the best person ever. And he has a young son here who we would never see if we lived in the USA, we would miss watching him grow up and having a close relationship with him. I really enjoy being a stepmom, and I can't imagine moving away from him. Plus, my mother in law has become one of my best friends and I love having them nearby. They are great people and they have always made me feel welcome here. They've been so supportive.
2. Weather - I like the weather here much more than Texas which is where I am from (if I say that to an English person, I get this response -

). It's just too hot there in summer, and there are some pretty extreme weather situations from time to time (tornados, flash floods, ice storms, and hurricanes and tropical storms down south) and I haven't been missing out on any of that by being here. I like the cooler temperatures here and having a real winter. Christmas feels more like Christmas here, because it's doubtful that I could be standing around outside in a t-shirt.

3. Employment - I do complain a lot about not being paid enough, and I think a lot of jobs here don't pay what they should. However, when you factor in that most people get 5 weeks holiday per year compared to one or two weeks in USA (on average) then it's a pretty sweet deal.

4. Closeness to Europe and availability of cheaper travel. Of course, you can travel within the US to many places for cheap, but its nice to just hop on a plane for 3 hours and experience a totally different culture from the one you currently live in.
5. Healthcare - yep, you said it. I sometimes didn't have insurance in the states, and when I did, it didn't often cover the few things I needed it to cover. There was always a carry-on with co-pays and paperwork and whatever. And the premiums were really expensive. I love knowing that here, even in the worst situation (DH and I both being made redundant, for example) that at least we would have healthcare. My mom had good health insurance, but is still deep in debt over a brain surgery she had nearly 10 years ago. It's good to know that we wouldn't have to worry about finding ourselves in that situation. (And this is the main reason DH wouldn't want to live in the USA).
And in general, we live in a beautiful little village by the sea surrounded by castles, so you know, that isn't too bad.

I lived in the city most of the time in Texas, so the change has been really good for me and I feel so much less stress now. I wouldn't say I can't ever imagine moving back to the US, but if I did, I would miss the beauty of this place more than I could ever say. I love walking on the beach every day in the cold wind off the North Sea... some people wouldn't enjoy that, but to me, it's exhilirating (and a great cure for a hangover!) I am sure there are far more enjoyable places to live in the US than the city where I am from, though, so it's a bit of an unfair comparison. Basically, if I ever did move back there, I would have to find some place new, because I now know that I was never truly happy where I was, even though I love my family and friends and miss them every day.