Post brexit UK has had trying times and economy is struggling. So is the case for most of western europe economies ( for example Germany has been in recession since the war). Jobs are scarce and with inflation people are avoiding these countries. 

All of above is immaterial if you get into a tier 1 college in UK and I assume you are very good at maths wanting to build a quant career. If both those are true you would get a high paying job in UK. This will be easier in US even with a tier 2 college. For high earners in Finance, state of economy doesn’t matter as there are always jobs that pay you top money. In mainland europe either these jobs don’t exist or pay quite low. 

There are some options that you may find in Netherlands and Germany but at senior level they prefer their own (white people). This is not true in UK and US.