> So if the system tells the landlords using it to do the thing that would increase rents if every landlord was using it

This is precisely what happened. Quoting from my comment at the time (https://news.ycombinator.com/item?id=39579488) --

Subscribing to a pricing data service: legal.

Using data feed to guide pricing and set initial figures: legal.

Agreeing, either implicitly or explicitly, to let the pricing data feed set the price floor: collusion.

Leaving units unsold and refusing to lower the price despite insufficient demand: usually a bad business decision, possibly indicator of a market failure.

Leaving units unsold to maintain agreed-upon price floor despite insufficient demand: collusion, market manipulation. Congratulations, you are a cartel.

Homeowners are usually the ones who don’t want more building, not amorphous landlords who have very little control over zoning and permitting in a place like the Bay Area.