The thing is, though, if Pennsylvania doesn't go Democratic, the election is over anyway. Kamala has no shot at without winning Pennsylvania. Shapiro, IMO, gives the Harris campaign the *best and most likely* opportunity to win PA (though, obviously nothing is a guarantee) because he is unbelievably popular in Pennsylvania, and not just among Democrats/liberals. His approval rating is jaw-dropping in this age of hyperpartisan politics.
To be clear, though, I'll be thrilled with any one of Shapiro, Walz, or Kelly in really no particular order. All three would be fantastic additions to the ticket. But I think that, as it pertains to Shapiro, if you can virtually guarantee that he can deliver PA, it's almost a no-brainer (to me).