89 was both the onset of the AI winter and a significant slowdown in the PC market. The PC market had continued accelerating until about 1985, the year after the Mac was introduced and the year Windows came out. It coasted for about 4 years, but by 1989 the PC market was well-commoditized, the winners (Apple, Microsoft, and Intel) were flush with cash that they were deploying on prestige projects like Copland, Dylan, and OS/2, the cost of founding a PC software startup had risen such that a couple guys in a garage couldn't do it anymore, and we were just getting a string of incremental improvements like Windows 3.0, System 6, the Mac IIFX and SE/30, etc. Sound familiar?
1972 I'm dating from the replacement of the Polaris SLBM program with the Poseidon one, though my uphill neighbors say that the crash actually happened in 1968-1969 (they bought their house as a foreclosure in that recession, after the developer went bankrupt). 1972 is also connected with the age of most of the housing stock here, and the end of the Vietnam War. Much of the Bay Area economy of the 1960s was connected to defense: Lockheed Martin was the primary contractor for the Polaris missile program, the engines & nuclear reactor parts for the submarines were built by Hendy Iron Works (then Westinghouse, now Northrop Grumman), the nuclear warheads themselves were designed in Berkeley and Livermore, the chips for ballistic missile guidance were made by Fairchild, the military personnel connected to the project were based at Moffett Field. When Vietnam ended and you got the 1970s economic & defense slowdown, it hit the Bay Area hard. A lot of the 1970s microcomputer companies grew up against that backdrop: you had lots of electrical engineers looking for jobs, abundant new construction that was sitting vacant, and a welcome place for counterculture ideas.