The US push for the T-65 cartridge (that became 7.62NATO) and adoption of the M14 fucked over the Belgians (and the yanks themselves) far more than it fucked over the Brits.
The US needed the Belgians to vote in favor of adopting the T-65, and so the US promised the Belgians that they would buy FALs from Belgium, if Belgium voted in favor of the T-65. The Belgians agreed and suddenly 7.62mm NATO was a thing. But the yanks had never planned to actually buy the Belgian rifles, they were dead set on an M1-based rifle since they were sure it would be much cheaper to produce. You see the Americans were convinced that M1 production lines could easily and cheaply be modified to build the M14. To make sure the M14 got adopted they rigged the rifle trials against the FAL by using an incredibly shitty copy built by H&R using blueprints incorrectly converted to US-measurements.
They made sure the M14 had well over a year and an entire team to work out any problems with the rifle. The H&R team had less than 3 weeks and two guys. The H&R team was not allowed to actually attend the trials and tinker with their rifle, the M14 guys were. And then just to make sure the FAL-clone failed, the Army fucked over the FAL even harder by downright cooking the books on the trials report. Some of their cheating was incredibly obvious, for example they wrote that the M14 was more or less impervious to mud.
Well then it turned out that the M14 was pretty shit, the T-65 cartridge was overpowered for use in full auto rifles, and they never saved money by converting old M1 factories to building M14s since it was deemed nigh impossible and all the tooling for making M1 rifles was obsolete, worn out, and needed to be replaced anyway.