If I was deciding to attend a conference, I would 100% prefer to attend one where DHH and other pioneers are organizing/speaking. And also one that had more meat rather than the "softer" topics as you suggested.
And I 100% agreed with their "No politics at work" stance.
I had a policy in our company against discussing politics. I used to say some variation of "We provide products & services to our clients, and they pay us money to do so. Our politics or our clients' politics don't matter." (And it was easy to make this statement because there was no chance of our product being used by authoritarians or something, we were building software for COVID response).
So we had a hard rule that there would be no political discussions on company "property" (company slack, company emails, etc), exactly what 37signals had. If you want to text each other personally, go right ahead.
Nobody seemed to have an issue with it.
So in a nutshell, sounds like the personal political views (and attitude of partisanship) of the organizers ruined the conference.