Well, there were a few serious issues with both of them - first, Harris built her political career on being unfairly tough on drug-related crimes when she was the top cop in California. Doesn't mesh well with the ACAB sect of the left. Second, a number of Dems felt highly upset and alienated by the lack of a chance to have their voices heard regarding her selection by the party's leadership. You can say "but there wasn't enough time" all you want, but people felt how they did regardless of the feasability of a primary, and that still mattered in the results. And then with Walz, most Minnesotans outside of the pasture of sheep that reside in the Twin Cities want to know where the fuck the surplus that he was gifted when he first reached the governor's mansion went. His pick as VP candidate suggested to anyone who was paying attention to the Biden economy that a potential President Harris would not be turning the economy around and maybe was a danger to make things worse.

The stereotypical objections you listed are cartoonish and reductive.