1) Immigration
1) Health care
3) Living standards (some part cost of rent, some part accessible lifestyle, some part relationships and future plans, etc)
I'm a London programmer and yes immigration is an issue, but health care (for themselves and their partner) is joint #1 on that front. It's hard not to look on US healthcare as being the worst possible product of US politics and that starts to impact the standard of living thing.
Most non-US programmers I know come from societies where we're happy to pay more in tax to have a more civilised society and life. You may fix immigration, but to make the US an attractive place to want to relocate to far more needs to be fixed.