If my memory or knowledge doesn't default me, between the end of the 60's and begining of the 70's there was an amazing flow of lenses, including zooms, and system parts, by the big manufacturers of that period.
Yes, I believe that is true. This was my era as well, being in my late 40's now.
But consider that at the time, cameras were durable goods. Yes, manufacturers wanted to sell bodies, but for many, a body once purchased was considered to be good for maybe a decade or more. Most of the amazing technological advances which caused people to buy new camera bodies had happened - instant return mirrors, TTL metering, and even AE for those who wanted it. AF was still some ways off.
So I believe the manufacturers concentrated on 'system' building. Now you had the body, but did you have the eleven different flash units they made? All the lenses? Winders and so on? It was a mad dash to see who made the most - and best - accessories.
This is not what i am seeing now, quite a few years since digital cameras are on the market. But, as stated, i am a big ignorant here.
I believe digital cameras are more of a commodity item now. This is not an indictment of digital; as you know, I love and use both film and digital. But my four-year-old *ist DS is considered pathetically out-of-date now. Doesn't bother me, but in honesty, after 50,000 shutter actuations, it probably is time for a refresh.
While my 1962 Canon FX just had a CLA and is ready for another 40 years service...
What I do enjoy about the digital era is how cheap it has made my beloved mechanical cameras and lenses, and how the technology for digital keeps evolving and becoming less expensive as well. It's strictly a win-win for me. My camera body does not have anti-shake or face-detection or a gazillion megapixels, but that's OK; when I next dip a toe in the water, that will be on the list of standard capability at the price I paid four years ago.
Point is - when the camera body is a commodity item and not a durable good, the manufacturers have to put their efforts into making camera bodies and innovations in digital technology and not as much into the 'system'.
Now, this or that folk can claim how wonderfull he is doing in adapting this or that prime manufactured some 30 years ago, but my instinct tends to tell me, that digital specialized lens should be better than any adaptation. Specially, digital primes.
I feel that my Pentax *ist DS kit lens is a fine lens. Not well-made in the traditional sense of my SMC manual focus primes, but the image quality is acceptable to me and it has proven to be durable enough for my needs.
However, to compare quality of construction, the older prime lenses of brass and glass win every time. For critical examination of output, I still believe the older primes are superior, but I may be biased. They're certainly faster (at least the ones I can afford) - and that's important too.
I hear you. I am wearing a 1970's era Seiko 5 mechanical wristwatch. I have a $30 USD Casio that keeps better time. I wonder why I wear the mechanical watch?