Manufacturers past their heyday

Wow, you youngsters do not know much audio history. There is only one company that I can think of that is around today that is not near what it used to be in terms of the product it makes.
Saul Marantz started a company in 1952 with a preamp he built in his kitchen, The Consolette. By 1965 his company was the undisputed maker of the finest audio gear in the world. It was also the most expensive and the best looking. He created the formula that dozens of audio entrepreneurs would use in the future to jump start companies over and over again, Mark Levinson, Dan D'Agustino, Nelson Pass, etc. The beginning of the end was in 1964 when Saul sold out to Sony Superscope. By the mid 70's Marantz was reduced to making high profit cheaply made mass market receivers. Their best equipment had been overtaken by newer marks and no more would you see Marantz the cornerstone of high end audio stores. 

Just like Marantz, KLH is another in name only. Sure ain’t the same company that Henry Kloss started.
https://klhaudio.com/

One of my father's friends was Rudy Bozak. In the late 1950's, he made my dad a custom pair of Bozak speakers. We lived in Connecticut close to where (Dr.) Bozak had a facility - he was a great fellow, and I do not think that his work was archaic during the time in which he lived, but I am not sure whether his brand lived on in any manner.

S.A.E., Harmon-Kardon (I guess Harmon lives on as a conglomerate but the celebrated “Citation” line is a relic of the past.), 

This sounds more like a marketing question. There are fewer high end audio stores that we can just walk into and listen to gear. Then the ones that are open have their favorite brands they carry. These brands have to be ones that bring people in and ones that they can sell at a margin that will pay the bills and they need to make a living selling them. Just as your question is positioned as companies that have fallen from where people used to perceive them to be I will say that there are companies out there that have been hyped way above what their quality really is. This is marketing 101 and marketing cost money. Some companies are content to let their product speak for it self.