Those sound like very hard to work with lenses.
Woah there. Blatantly untrue. They aren't "very hard to work with", they just require a little bit more effort on the photographer's part, which past photographers have done for generations.
And that's why a lot of people avoid them.
People don't "avoid" these lenses, they are around 50 years old and not even an option to buy new on the market. Someone looking for a modern AF lens is in a completely different market from someone looking to use their old lenses or explore vintage glass with a lower budget. No competition or avoidance there.
Reason some are more difficult to work with is because they are not designed for speed. They are designed for shooting in controlled situations where you have total control over lights, subject matter, and movement of camera. In other words, they are designed for situations like portrait shooting.
Not true in the slightest. Either know your subject matter or do your research before answering questions like this! These are both 50mm standard lenses used as either kit lenses or upgrades to kit lenses. In the time that these lenses were built, 50mm was the default focal length used for 135 film cameras with interchangeable lenses, which is part of why it is sometimes called a "standard lens". 50mm was the equivalent of a modern kit zoom. These lenses built for general purpose photography, not specifically a studio or portrait situation.
The Jupiter 8 was built in LTM (leica thread mount) for Fed and Zorki rangefinders (bootlegged and upgraded pre-war Leicas). At the time that these were built, a rangefinder was much faster in operation than a TLR or larger view camera. In fact, by production of the FED-2 and later FSU cameras, they had improved controls and interface over the original Leica iii they were based on (combined viewfinder/rangefinder, more shutter speeds, improved film advance + loading, wider rangefinder base, and self-timer). The Leica rangefinder system was an early 35mm film system built specifically for portability and ease of use of use in varied environments outside of a studio. Your statement about the lenses only being designed for studio portraits could hardly be more untrue.
The Kalimar was built for the Yashica C/Y mount, which was an SLR system. This could be used for many different purposes and was designed for general purpose photography. Again, the Kalimar lens was designed for varied general-purpose photography, not just controlled studio work.
Modern camera lenses on the other hand, are designed to keep up with the technology of modern cameras.
Well, yes. That much should be obvious.
Thus, they are equipped with motors for fast AF speed and accuracy, stabilization for low light,
That's kind of the definition of AF and IS.
larger apertures for subject isolation and shallow depth of field
The two aforementioned lenses have a maximum aperture of f/2 and f/1.7, that's pretty fast and just as fast as any modern lens. For the record, Canon manufactured a 50mm f/0.95 lens over 50 years ago, so modern lenses don't have wider apertures than legacy glass.
, electronic manual focus for even more speed & egronomics,
Manual focus by wire is inferior to a physical connection by all metrics. Good focus by wire implementations can work alright, but a full physical connection will always be more precise and give immediate feedback. Focus by wire is only required due to the construction of AF mechanisms.
and can communicate with the camera for faster more precision on many options for AF set ups.
A lens has to communicate with the body to use AF. I'm not sure what your point is here.
Thus, that's why the lenses you have are difficult to work with.
Because they don't have AF or IS? That's not really a good reason. Note that the OP didn't say that their lenses were difficult to use, just asked why one was harder to focus than the other. For certain applications (landscape, street, low light, etc.) manual focus may actually be easier than trying to lock AF before every shot.
And why people will pay a higher price to use high tech lenses on modern cameras.
Not really. What you are paying for with a modern lens is a new item tax, improved optical quality, and and AF + IS. I would hardly call most modern lenses "high tech".
There is no right or wrong choice for everyone. And the options for what works best is only determined by you.
Agreed.
Also know that skilled photographers once used similar lenses you have to get great shots. They had to work harder, and have more photo knowledge and skills, but they were successful with those tools.
Yes, agreed!
You didn't address the OP's question about why one lens is harder to focus than the other at all. You just pulled a lot of fictitious negatives about legacy glass out of thin air (not to say that there aren't plenty of legitimate ones you didn't mention). Please think through your responses before providing misleading information like this!
