Is it about the product being ubiquitous and all pervasive?
The answer would be a simple yes, since every household had at least one.
Is it about the quality standard of the product?
The answer would be yes and no. The large majority of turntables served the purpose of playing records, but were of mediocre quality, indeed in contrast to the high quality of the recordings and the records themselves (like those 50’s and early ’60’s blue notes, Decca’s, RCA living stereo’s, etc.)
At the same time the brands that dominated this record player mass market also manufactured statement products to secure their reputation and boost sales of their cheaper products. Even after 40 years or more these state of the art products are still the ’golden standard’ for many audiophiles. We all have our favorites: the big EMT idler drive, the big Japanese direct drives, the big Micro belt drives, the Thorens Reference, etcetera. So yes, it was also the Golden Age of the (serious) Turntable.
Is it about the profitability for the manufacturers?
Record players sold by the truckloads and obviously made a nice profit through their economies of scale. But I would say that today’s market is the real Golden Age of the Turntable Manufacturer.
In my country The Netherlands we say that the 16th century was our ’golden age’. It was a period of international trade and great wealth accumulation, albeit only for a very small group. Ring a bell?
Their wealth gave rise to the city of Amsterdam and sponsored the great art of Rembrandt and others. The global elite in our hypercapitalist world no longer buy portrait paintings from artists to show off their good fortune. They buy other ’trophies’, like boats, cars, wristwatches and, yes, turntables. So perhaps the 'Gilded Age' of early 20th century industrialist society is a more apt comparison.
Anyway, it’s a Golden Age for manufacturers of these luxury products. It took a while, but high end audio has finally managed to tap into this world. It explains the current exorbitant prices and - probably - large profit margins.