It's only because he (or rather, the people close to him) know that opening his mouth will make things worse. This has actually been the moment in his presidency where he has perhaps shown the most restraint. If he opened his mouth, you know he would say something vile and incite more riots. Trump being eerily quiet is leaving a profound leadership vacuum, but this is vastly preferable to his style of "leadership".
Biden always says weird stuff, and even though comments like the one you posted are certainly not helping, I agree he still comes out ahead. At least his stuff you can kind of laugh at because you know he just isn't thinking and won't double or triple down on a "Cops should shoot people in the legs!" twitter campaign.
They just need to script him some stuff a reasonable person would say and then rush him away to make sure he doesn't take any questions or ad-lib. Or better yet, have a joint address with our former president whose words are mostly likely to have a positive impact on the nature of the protests