It has nothing to do with public health and everything to do with keeping people out. Biden, like Obama before him, is taking the “moderate” position in order to reach out to voters who will never vote for him.
Infighting between those who support tougher enforcement and those who favor expanding access to the asylum system has hindered the administration's border policy, officials told CBS News.
Naively, based on what I notice in the media, one could add “maintain the support of people who have voted for him”. E.g., the first plausible hit I see on the web is https://news.gallup.com/poll/1660/immigration.aspx which gives the results of Gallup polls. Right now, “increase immigration”, “decrease immigration”, and “keep the rate the same” are basically tied at 33%. For “increase”, that’s the high point (since 1967). Given that about 40% of the population is declared Democrats, and 51% voted for Biden, at least 7% of Democrats and 18% of Biden voters did not choose “increase”. (And if Biden lost a few percent of his voters, he’d have lost the election.)
I, personally, favor raising the immigration rate to 4.5M per year. (If you have an hour to kill, I’ll tell you all about it.) But I’m clear-sighted enough to know that this concept is very unpopular.
Much worse is the consequences in places that have been generous to asylum-seekers. The asylees have generally been considered undesirable by the citizenry of the countries they’ve landed in. (And the cultural differences involved have caused serious friction in many cases.) Their presence has significantly eroded support for social-democratic norms in a number of countries, and increased political support to restrict immigration in one way or another. (e.g. Brexit, and I’ve read, a substantial contraction of the Finnish welfare state)