If the YIMBYs want to win they need to realize their opponents are not just homeowners. Low-income renters have issues with them too. YIMBYs are generally in some form of denial about that.
They like to believe that they are fighting the progressive fight against rich, old homeowners. They like to proclaim they are fighting for "poorer, younger, and (frequently) non-white people" (Stripe).[1] But when it comes to explaining why poorer and non-white renters aren't always on their side, YIMBYs are caught flat-footed. If they're not careful they end up sounding condescending. Like, Didn't you guys take economics? Supply and demand, bro!
That's probably why the bill failed. There were significant amendments added to address the concerns of low-income housing advocates, who see a greater need for BMR units among other things. But these were added only after substantial protest.
One low-income housing activist said it best: "The YIMBY movement has a white privilege problem."[2] They are kind of in denial about the effect of development-stimulated gentrification on rents in affordable neighborhoods. They like to think that young tech workers are in the same boat as minimum wage earners, all in need of "affordable" housing. They really don't like to think about things like induced demand, where adding capacity can actually create more demand.
In the long run even the tech industry needs affordable housing for service industry workers to support its continued growth. It's not just about economic justice or turning back gentrification. Quite simply, if cooks and teachers and artists can't afford to work here it's not going to be as desirable a place to live. If the market alone can't solve that -- and many low-income housing advocates believe it can't -- then we need to fight for BMR and other strategies to create and protect truly affordable housing.
[1] https://news.ycombinator.com/item?id=16988398
[2] http://www.latimes.com/politics/la-pol-ca-housing-bill-failu...