(I'm leaving aside the question of consultants, the vetting process, etc because I see those as answers to "how" we got here, but not "why".)
The first component was the generational handoff. Maine voters did not want to go with a 79 year old candidate to replace a 74 year old senator to work with a 76 year old leader in Schumer to fight the power grab by an 80 year old president.
Boomers: you've got to let it go, man. You have to pass the damn torch, or you're gonna take it to the friggin' grave with you. Remember RGB.
The second component was the desire on the part of the Democratic voter base to find someone who they believe will fight for them. Democrats have been so passive for so long (see Schumer's "harshly worded letter") they are dying to see someone actually stand up and do the actual work that voters put their representatives in elected offices to do in the first place.
The third component is the voice that is missing in the Democratic establishment, which is the voice of the left. Platner positioned himself very well in that regard and quickly became the progressive stand in despite his past (more on that below). This is a direct consequence of the Democratic establishment's inability to form a big tent. "Vote blue no matter who" has been a one way street with the Democratic Party, though I have to admit that the establishment was much easier in their embrace of Platner than they were, say, of Mamdani. That contrast is probably another layered cake on its own, including the types of positions in the play, the undeniable ethnic component, etc etc. One of those factors, I believe, was the next component.
The said component, the fourth, was the elephant in the room. Masculinity. Platner presented himself with a strong masculine profile from his military service to his voice and everything in between, and Democrats were much more willing to embrace that and assume that the bad parts came with that masculinity. This was a way to finally find some candidates that would put the "wimpy, feminine Democrat" image to rest, but guess what? Once you venture into a high testosterone world, things tend to get a little icky, and dirty, and somewhat violent. Masculinity is a tricky tiger to ride. You may start with William F. Buckley and end up with Enrique Tarrio.
The fifth component is the romanticism that is built into the liberal mindset. That old adage that Democrats fall in love, Republicans fall in love is 100% correct. Once they feel like they have found someone who will speak for them, Democrats can't help falling in love. I'll leave it at that.
The sixth and the final component at work, and the one that spoke to me the most, was our belief in the possibility of redemption. Not the religious kind, god forbid, but the secular kind. Belief that people can have a personal arc that allows them to put their past behind them and embrace a better self. That's what we hope for ourselves 24/7 whether we think about it or not. That's what, I would imagine, a lot of religious folks strive for. But most importantly, that's the hope we have for this country that we can ultimately get out of this nightmare somehow, once the fever breaks, and come back to a better place where we can once again, or perhaps for the first time in our nation's history, look at each other as human beings who are our equals, each with their own life story that is being written every day. At the end of the day, I see the hope of individual or nations; redemption as the only reason to have any hope at all.
Platner looked like he could have been that one person that validated that hope. Instead, he turned out to be yet another broken person who's still struggling with and succumbing to his own demons.
This has been a terrible episode, and hopefully we all learned something from it whether we were on board with him or not. There are a chock-full of lessons here for those who are interested in being reminded of them.