Minor nitpick, but I do not think you know what dense means.
Most cities are denser than Switzerland. My undergrad town of 25K is over 20 times denser than Switzerland.
Most cities are denser than Switzerland. My undergrad town of 25K is over 20 times denser than Switzerland.
Switzerland has excellent public transit. Therefore, if there is a density threshold to offering good public transit, an area would need to be at least less dense than Switzerland in order to argue that it isn't possible.
The SF Bay Area is denser than Switzerland. Therefore, the reasons for not having good transit are not to do with density, but with something else (politics, zoning, public support, etc.). But density is not the issue.