Perhaps Jan Smithers left Brolin after discovering & rejecting his true inner core - a radical leftist & adulterer seeking a “Streisand-like” mate.
IIRC, she moved to an isolated area of Canada for awhile to get away from Hollyweird and all of its connections.
I recall reading that Smithers said BS always treated her kids w/Brolin wonderfully. So that’s a good thing.