Democrat party poohbahs decided the 2024 election is probably a loser. They see Trump has consolidated the Republican party in 2024, and I estimate that internal Dem polling is not looking good for Kamala. They also see that there are several very strong young Republican candidates completely in the Trump movement who will make very formidable candidates in 2028. These include J.D. Vance, Ron DeSantis, Sarah Huckabee Sanders, and Vivek Ramaswamy.
Because 2024 looks like a loser, the Democrat poohbahs are going with the B-team. The far-left Tim Walz pick is a nod to the hard left in the party and a hard lurch in that direction. The party will give a strong effort for the ticket, but if it loses (and my guess is they think it will), the hard left loses and the party moves to the center in 2026 and 2028 with new candidates like Shapiro. I think the Democrats see 2024 as a sacrificial election and are holding back their strongest stuff for 2028.