It probably is the case that no one back then even thought of a phono stage as a separate component; that would explain the dearth of examples. Back then, no one thought of power cords as discrete components either. Also, the popularity of low output cartridges is a modern thing; their would have been no need for phono stages back then to work with such low output.
Phono Stage - The great analog tragedy
In the world of analog playback, there is an interesting observation. There has been tremendous innovation in the field of
Turntable - Direct, Idler, Belt
Cartridge - MM, MC, MI
Tonearm - Gimbal, Unipivot, Linear Tracking
For all of the above designs we find some of the best reference components designed in the 50s, 60s, 70s and 80s. Most of the modern products are inspired from these extraordinary products of the past. But when it comes to phono stage, there is hardly any "reference component" from that era. They just standardized RIAA curve for sanity and left it. Manufacturers made large preamps and amps and allocated a puny 5% space for a small phono circuit even in their reference models, like a necessary evil. They didn’t bother about making it better.
The result? It came down to the modern designers post 2000 after vinyl resurgence to come up with serious phono stages for high end systems. Unfortunately they don’t have any past reference grade designs to copy or get inspired from. Effectively, just like DACs, reference phono stages is also an evolving concept, and we don’t have too many choices when we want a really good one which is high-res and natural sounding. Very few in the world have figured out a proper high end design so far. And most of the decent ones have been designed in the past couple of decades. The best of the breed are probably yet to come.
It is a tragedy that our legendary audio engineers from the golden era didn’t focus on the most sensitive and impactful component, "the phono stage"