In the case of well-funded, highly-respected agencies such as the FAA and EASA, it makes a lot of sense for other agencies to follow their lead especially when it comes to acting on the side of caution.
Any aircraft the FAA or EASA revokes certification for, or demands action for, is at immediate risk of being grounded by other regulatory agencies as these decisions cascade from one agency to another.
It's worth it to put the cost of agencies such as the EASA or FAA into perspective. For the FAA:
For FY 2020, a total funding level of US$17.1 billion will enable the FAA to achieve its mission while making critical investments that support innovation, protect aviation safety, and make investments in our nation’s infrastructure.
By contrast, the government of Namibia (a country with a rather smaller population - well under 3 million people - than the USA's) spent a total of USD 2.3 billion in 2019, while Namibia's GDP was USD 15 billion.
Not only would Namibia gain absolutely no advantage in doing anything other than following the lead of the EASA/FAA, it simply doesn't have the spending power to achieve much in that area anyway.
(It remains to be seen whether the FAA's reluctance to ground the 737 MAX has a long-term effect on its international standing as a solid-gold reference for international aviation safety.)