If you want to operate globally you have to accept the laws of the places where you do business. You can't just say "but HQ is in 'merica so screw you" and expect to continue trading in those countries.

Any one of these countries can block a merger if they see an antitrust issue; Qualcomm and NXP found this out the hard way with China a few years ago, and Microsoft and Activision Blizzard are finding that out with the UK right now. Of course, these companies could flip off China or the UK and just merge anyway, but then they'd risk being subject to crippling fines, having their local assets seized, and even being barred from doing business in that market altogether.