It's all about cost and cost is more than labor. ARM chips in particular are driven by cost and while Intel can demand and get more than $100USD for a single uP what's the cost of a typical ARM processor? Intel can't compete there either.
The major FAB's that produce them are running 24/7, but so are almost all FAB's -- the only way to cover the multi-billion in capital cost is to utilize the equipment 24/7 and almost all FAB's do this. But, like many things in production, the 1st world is at a disadvantage to the developing world because the pay scale is higher and the workplace safety and pollution controls add cost that companies in other parts of the world don't have to deal with.
This is all part of a bigger picture and although it makes sense to the bean counter types to close domestic production and move where it's cheaper, but we've seen that model before and the end result is the disappearance of the domestic companies that outsource. In the mid 60's the USA produced about 95% of the worlds TV sets but by the mid 60's the big TV makers, wanting to cut cost on products that were very labor intensive as TV's of the day were owing to the discrete components that they were made of, and they began to outsource to Japan. Within a decade Japan owned the market and by the early 80's there were almost no TV's being made in the USA and the companies that moved production to Japan were also history -- replaced by Sony etc. The US makers of TV's had bad timing with this move as the move towards integration, pioneered by Ti and a few others in the semiconductor business dramatically lowered the cost of TV set production independent of labor costs. The Japanese benefited from those advances and the US companies were, by then, on to something else.
So, it's a more complicated picture than simply continuing or discontinuing domestic production but the end result has been demonstrated before and will/is happening again!
Brian