I honestly don't know, but I think Biden's issues with aging have overshadowed... this.
This isn't new. His schedule has been light this entire time, his rallies have been even more insane and incoherent, he flubs more than he used to, etc.
And for as much as him and "Substitute Pence" talk about Kamala not having a press conference, outside of that disaster-class NABJ debacle, he hasn't had one of those in months either. He spends all his time in safe spaces (like Fox and with other right wing media outlets/figures)
It just didn't get noticed until now more broadly when people are sizing him up against a more youthful candidate. That's what we are seeing here IMO