[danabrams]

Here's a theory...

Although illegal now, San Francisco used to have a widespread practice of "key money"--a bribe you paid the landlord to choose you to rent the apartment that due to rent control or other factor was priced below market demand.

Because the landlord was capturing the extra value directly, a cultural practice of high broker fees never developed there, while it did in the east, where bribes were less common. Thus someone other than the landlord captured the excess value.

It's also entirely possible that the broker's fee is being illegally passed as "key money" to the landlord in a way that's harder to detect/litigate in NYC because it's not direct from the tenant.