I suspect that what happened to a lot of the small brewers is similar to what happened to Schlitz.
1953: Strike by Milwaukee brewery workers hurts brewers like Pabst, Blatz and Schlitz, which lose market share to rivals such as Anheuser-Busch Cos. Inc. of St. Louis.
1954: Schlitz briefly rebounds to again be the world's best-selling beer.
1955: Anheuser-Busch takes over the top spot, which it still holds.
1975: Immediate family management of Schlitz ends and distant relatives and outsiders take over the operation.
Mid-to-late 1970s: Schlitz still sells well, so the new owners try to make more by shortening the fermenting process. But the beer has no foam and is flat, so managers add a seaweed extract. But that turns solid after sitting in bottles for a few months. Schlitz sales fall and the old formula is gone.
1981: Production of Schlitz ends in Milwaukee when workers strike.
I remember a Harvard School of Business case study which concluded Schlitz's decline and failure was because the beer tasted bad.
Pabst owns the Schlitz brand these days and supposedly has reintroduced the original Schlitz beer. I'll have to see if I can find some to try.