Personally, I think it came down to just a couple people in the campaign thought the abortion issue would bring every single women to vote, who at the time allegedly outnumbered male voters and said, "Hey, lets have Harris run, you know, a woman who women can vote for because she knows abortion stuff. Easy peasy."
To me it was a decision by just a few main campaign people. I'm truly sorry it didn't work out like they thought.
Painfully, sadly sorry.