[hotsauceror]

Why would a private developer's decision not to include parking, be interpreted as some kind of metric for the sufficiency of public transport in the area?

If a builder chose not to install locks on the doors of a new apartment complex, would that be "a good thing because it would indicate public safety is good enough that people don't need their own private locks for most areas?"

There is no incentive for them to consider these externalities at all. There is, however, an incentive to use that same space for something they can profit from - namely, additional apartments.