Kamala is not an established progressive, and is in fact in the process of moderating even further to the center
Balancing the ticket with someone with more distinct progressive bonafides isn't going to lose the election, especially if that person "codes" well like Beshear or Walz. No one is asking some blue haired lesbian in Bushwick to be the VP. Shapiro has taken stances that are genuinely offensive to groups within the Democratic coalition, it's completely fair for them to let their preferences and disdains be known during the selection process.