Healthcare, property tax, the school system, the climate, the cost of living, transportation, social conventions, religion, vacation allowance, long-term financial security... I'm not saying any of this is all good or all bad, just that it is a very different country, it's not your home, and it's vital to take a clear-eyed view of how exactly it would work for you.
^^This is the truth
OP, I'm American born but have been living in the UK for most my adult life. I've got to be honest, what you describe about loving America sounds like it is coming from the perspective of a holiday-maker.
IMO America is great to travel and holiday in but not to live in unless you are very wealthy & white and even then there are still major issues. I wouldn't go back to live there if I had the chance because reason my whole life is in the UK but the other main reasons are:
WORK LIFE BALANCE SUCKS: Are you prepared to only get 1 week of annual leave a year? If you're lucky 2 weeks? If you do get that and take it then be prepared to be made to feel guilty about it. Sick leave? Let's hope you're employer is somewhat decent, I've known people get fired for taking sick leave if their employer felt they needed to be in work. If you have children then good luck coping with any kind of crisis with your employer. This is known issue with America as they do not seem to grasp the concept of a good work-life balance.
HEALTHCARE: This is obvious but its expensive, even with insurance. Do you have enough money to cover any accidents and illness? If you need an ambulance then be prepared to pay for one and God forbid you have anything horrible happen in your family such as cancer or any other serious illness as it could take you into serious debt. The medical insurance is costly and wont even cover anything. It disgusts me how greedy the medical industry over there is- making money off of people's health & misfortune.
ATTITUDE: People will say Americans are friendly and they do appear so but it really is a faked happiness. They are much more focused on appearances and how they are perceived then actual honesty. Think "Perfect suburban white picket fence" That doesn't really appeal to me
RACISM: This may or may not be relevant to you, I don't know. But it is an major issue (I struggled with it whilst growing up in America) and with Trump it really is not getting better
GUN VIOLENCE: I have friends in America who are planning on home schooling their children because of the risk of a school shooting, and this is in the nice, upper class areas. When I was growing up we didn't just have fire drills, we had to practice what to do in the situation of a shooter- again I grew up in nice middle class areas. Look up the statistics for how many shootings happened in the first 3 months of 2018. Its awful.
I'm sorry if this is a long and miserable post. If it is truly what you want to do then go ahead and do the research. It is a lot more expensive to live in American than the UK. The desirable locations you have mentioned (such as California) are even more expensive. You need to think about all the costs included and need to have a good paying and stable job lined up before you move.