The only reason my Canadian cousin gave up his dual US citizenship was because when he was 18 and the Vietnam-era draft was still in place he could be arrested for not having registered with the US Selective Service if he crossed the border. My aunt was a US citizen and I think all of the kids were born here; her husband had Turkish citizenship and they had to leave the US and return every year to do with visa stuff. They eventually settled in Alberta to avoid those hassles. There are many instances of dual citizenship if you look around.

The US has learned a lot about the cost of security details since 2017 when Trump was sworn in. His golfing trip count is up to 243 at a cost of $122,000,000 to the nation. General Accounting Office report information. He travels with a large family entourage, does nothing to be inconspicuous, and is probably drawing those funds in a way that enriches him (the Secret Service has to pay the market rate for the rooms they use in his resorts, his hotels, etc.) I suspect Meghan and Harry, who have a better sense of proportion, would cost a lot less.