Earlier quoted context omitted.
EU pre-ordered more Pfizer than the US. Enough for 150 million people in EU, vs enough for 50 million in the US. The US has ordered more after it was approved.
The EU did not pay as much as the US — and signed the contracts much later. Pfizer is doing the rational actor thing and, given a shortage, prioritizing their highest paying clients. There might also be verbiage in the US contract to this effect. Also, Pfizer is an American company.
BioNtech is a German company. If it would come down to national egotism, BioNtech would just kill the licensing deal and Pfizer wouldn't be allowed to produce anything.