Any reason why they should?
Plenty of reasons. But they were betraying us long before the Obama years.
Any reason they should?
Other than that America provides for their defense and rebuilt them from ashes and bailed them out in two world wars and then protected them from communist dictatorship and that America is a western democracy which actually believes in the rights of man and that the US Navy keeps the sea lanes open and that the US has ensured the free flow of oil out of the Middle East? Other than that, no particular reason.