Earlier quoted context omitted.
More supply also increases traffic. This isn't just about everyone worrying about their housing prices (there are a lot of NIMBY reasons beyond that).
More housing where the jobs are creates less traffic. Putting your jobs in Berkeley and your housing in Vacaville is what creates more traffic. A Berkeley with 300k people - which is the population that would support the number of jobs already in Berkeley today - would have noticeably less traffic. Same for a San Francisco with two million people etc.
WFH works also, but then you don’t need to be near where your jobs is.