Different approaches, but I have to say with the advent of mirrorless cameras and the ubiquity of different adapters that allow all manner of "frankencams" to be used has broadened the appeal of
any good glass. Certainly Pentax was ahead of the curve as natively the glass can be used directly, but it can also be used in a similar manner with mid-high end Nikon gear.
I'd say there are the some for whom the shooting style matches the subject, such as macro work, those who maintain mixed film and digital media to whom older (or modern as per
Docrwm above) manual focus lenses make sense (and allow valuable dollars for actually getting to shooting locations!). There are also those generally curious who want to try a focal length or particular lens in this camp. Astrophotographers too (where AF makes no sense) also tend to use MF, or older glass.
All that being said, usually the newer lenses are better designed and coated for digital sensors, and often the better older glass is priced within the same $X00 range, plus you get AF, which can be very useful. I don't know for example whether I could now get rid of my 18-135mm, or 60-250mm, the former as it is a flexible "beater" lens, and the latter as it is just so good.
To finish (my ramble), I think that the proof is in the pudding. Rhetorically, are you getting the results for whatever photographic interest you are applying your kit into? I'm also sure that as
Docrwm comments above that ignorance is a factor.
Personally, I've been into this
obsession interest (I've never been interested in commercial work) for around 20 years, and in that time have gone from a 110 film snapshot shooter to a medium format snob to somewhere in the middle in digital land. Early on it was all about documenting travel, then playing with the advent of digital and learning to post-process, then diving, then printing, then family portraits, etc. The journey isn't over. While forums are a great place for information, IMO, they are also full of individuals, from different countries, who hold different viewpoints, that I suspect differ according to where they are on their own journey. Each has their own budget and tolerance for results.
I have both (MF/AF) sorts of lenses. This afternoon I was using a Fuji X-E1 with a Minolta MD 100mm F3.5 lens that has ten years on me for age. It's a beautiful piece of kit, that is great wide open. However, this afternoon was a bit dim, and I should probably have used the 18-55mm kit for the IS/shake reduction. Then again, the subject motion was pretty high, so maybe I just should have cranked the ISO.......
Digital does give one lots of choices.