I recall that training in the US does not attract 'VAT' in the same way as hire will, whereas in the UK VAT is 17.5% of everything and no breaks.
The hire and training costs (and cost of fuel) is lower in the US and many other countries as well.
On the other side, the reason that all the UK schools do not close and everybody goes to the US is because not everybody wants to; the visa system makes it hard; people have homes and other jobs to help fund the course and we like "Blighty weather" because that is what you'll end up flying in when live.
h-r