I've kinda come to the conclusion that it's a combination of how they really hate how Walz codes (ie. Normie Midwest dad, teacher, coach) and that because Vance has been attacked hard, it warrants an equal reaction / pretending he has equally grave flaws as a candidate (he doesn't).
As the old saying goes, when you're the hammer, everything looks like a nail.
But strategically, Adam is right... We are now in the third week of the Trump Camp Pain focusing way more fire on the VP candidate rather than the actual candidate. It's just really not smart at all