Border enforcement is 100% at the discretion of the executive. This is something Biden could have mandated with an executive order. You may have noticed he issued many of them yesterday.
Biden isn't still trying to find the bathroom and learn how to use the photocopier. His team has been preparing for months for this moment. The lack of action here is a deliberate choice.
Yeah but he can't do EVERYTHING in the first day, even executive orders an no matter what he hadn't got around to, you'd be screaming about how that should have been a top priority for him.
Because you want him to fail. You'll bluster and act all faux-shocked, but that all it is. You didn't get your Progressive uprising, so you don't want Biden to succeed.