I talked to a board member of one of the Bay Area transit agencies who had some interesting insights into the situation. From his perspective, the path toward improved connectivity starts very small.
The technical reason for poor connectivity in his region is that the buses are not on the same schedule as the train. For example, trains run every 20 minutes and buses every 15 (it could be the other way around, I don’t remember) But in order to synch up, the bus agency would need to run more buses, and that costs hundreds of thousands of dollars. They can only cost-justify that with additional ridership.
How to get additional ridership? They went to their marketing person and asked her to run a marketing campaign. She said, “what can I market, the buses are always late. The best thing you could do would be to improve on-time performance.” So they sent trouble-shooters to the branches, to understand the reasons buses run late and fix the problems.
So, from his perspective, the single biggest thing the agency can do to build constituency for better connectivity is to get the buses to start running on time.