How much are you willing to pay for screening a very long list of diseases - both in administrative costs and traveler time wasted? Will you be quarantining citizens too, as some infections have an incubation period before they can be detected - who will pay for all of that? How many tourism dollars will be lost due to this additional friction?

Now that we have established you're willing to pay to prevent diseases spreading to the US, why do you think that screening at the border is superior to reducing the worldwide incidence, or eradicating them and never having to screen for them ever again?