The issue stems back to 2016. The Democrats planned on 8 years of Hilary and did not feel like they had to have another viable candidate until 2024. Trump won the election and it set off a firestorm in the Democrats because they needed a new popular candidate that they did not truly believe they would need to have for the 2020 election. Then it gets made worse in part due to their effort to derail Trump in the perception of the American public rather than focus on finding someone that independents could get behind.
Michelle Obama was probably their choice to groom for 2024 but the private sector of making money off of political influence has been nice to the Obamas, post-White House. Furthermore, Democrats need a candidate that is genuinely appealing to the old guard as well as the new guard of progressives. Remember, many Democrats are old-school farmers and they are grounded in their faith and service toward people, and not many can relate to the new "woke' ideals of the younger generations. Harris just is not relatable to people overall because she comes across as fake, disingenuous, and condescending. (Yes, I understand that Trump fits that mold).
All in all the Democrats are probably in more disarray than they would like to admit to right now. These individuals will not be considered, but could bridge a gap to the 2032 or 2036 elections: Steve Bullock, Joe Manchin, Andy Beshear, Josh Shapiro. Moderate, moderate, moderate...