How long ago? The N-Judah trains are packed like sardines inbound in the morning and outbound in the evening. They've started running empty trains out to Hillway because typically by UCSF the inbound trains are completely full. More housing in the Sunset would absolutely require improved transit.
MUNI has added extra shuttle trains that just run the busiest part of the line (https://www.hoodline.com/2016/09/new-n-judah-shuttles-aim-to...), and the N-Judah will be the 1st line to get 3-car trains (https://www.hoodline.com/2017/02/n-judah-will-be-first-line-...).
But yes, they could run even more. And there should be far denser housing near dedicated rail lines.
I'd go so far as to say all lots, statewide, that are within a 5 minute walk of a rail station should have no height or housing-type restrictions other than those required for earthquake safety. (And yes, this goes for the commuter suburbs, too. If you get a BART station, you need to accept a bunch more housing – or the trains should skip that stop.)