Santander offered 3% up to £20k to all customers on their main checking account but had to cut that rate in the end.

They had some sweet deals I was making just under £20 a month on cash back plus a good (for the time) interest rate.

But the half baked eu ruling on merchant fees screwed savvy investors and the banks found another way to charge merchants.

Tesco's 3% is ongoing, it is limited to £1500 though, I've had one for 5? Years. Was only guaranteed for 12 months, and guaranteed it again when they had their security breach a few years back.

They have limited account opening at various times though.

3% in the UK on GBP is different from 3% in the US on USD. You can't really compare them.

3% is 3%. 3% on £100 = £3. 3% on $100 = $3.

If both banks invest in whatevs (local currency) paying 5%, then they get 5%, pay you 3% and make 2%.

Are you trying to reference relative inflation?

Or something about the USD makes it difficult to invest?