I know a bit about the thinking here. I write COVID related science notes on another forum I belong to. I'm a retired PA and follow this stuff closely. The science based facts on the effectiveness in preventing the spread of SARS-2 by isolating infected persons is well established. Quarantine of persons potentially exposed but not necessarily infected (i.e., they have not been tested for COVID-19 by PCR or RAPID Antigen testing) has become a standard public health measure employed in some locations but not all. It depends. Implementing such approaches involves cost/benefit analysis as well as assessing the scale of such an undertaking. Most Caribbean countries are already doing this deciding that they will open their boarders to unrestricted international arrivals and then, in some cases, track or test and track. The scale is smaller than it would be in the US or EU and is driven by the need to re-open tourism economies.

Right before Trump's departure from the presidency, he rescinded a host of travel restrictions that upon ascendency to it President Biden cancelled those rescissions. It is clear that as of that rescission and the language of his EO, yes, you will need evidence of negative testing at the most 3d prior to boarding a US bound flight from a foreign county (to include US territories) and you will need to quarantine for 7d upon arrival in the US. Personally, I don't think the 7d quarantine derives significant enough benefit in terms of risk reduction but it isn't unreasonable. In the current circumstance where Biden's messaging/signaling is such that it is, were, going to see more mandated mitigation.

The thinking here is in keeping with Joe Biden's approach to his pandemic response in the US. Implement measures that will reduce the introduction of newly infected persons arriving from outside the US to as near zero as possible. Interstate travel also risks increased transmission, especially IVO the emergence of SARs-2, B1.1.7 - a proven more transmissible variant of SARS-2 already in the US. That's why this is mentioned in the linked article as well. Even though the measures were discussing here may not be as useful as quarantining people who are known to be infected, it is nonetheless a reasonable public health measure - albeit a butcher's knife rather than a scalpel - and it's in concert with the CDC's position (quarantine people arriving from outside the US at all ports of entry, don't travel if you don't have to, don't cruise).

There are better ways to do what the Biden administration wants to accomplish to mitigate viral spread that have to do with expanded RAPID Antigen testing and genomic sequencing of collected samples with appropriate follow-up for that after testing. The guy you want to absolutely quarantine is the traveler with a positive RAPID Antigen test and then on lab based test result is found to be infected with SARS-2, B1.1.7 or SARS-2, B1.1.35. At the very least administer RAPID Antigen tests to arriving travelers and direct home care and quarantine as appropriate. Some airports in the US, GB and EU are already offering RAPID tests to travelers that want or need them. The means and resources are there to mandate it on a wider scale in the US but not for genomic testing - but that need is being recognized and reportedly addressed. Vaccine pass-ports, or equivalent and pre-boarding and post disembarkation testing are probably in the future for all international travelers, possibly domestic as well. The introduction of that is going to be cumbersome and inconvenient at first, like this one is, but will streamline over time.