I could say it is a personal idiosyncrasy. I could say, it's because under my normal shooting conditions, an EI of 160-200 lets me use the shutter speeds and apertures which I preffer. In fact, I did say that in my opening post and again in post #24. So I don't know why you keep asking me why.
Is wanting to find a film+developer combination that lets me use my preferred camera settings really such an out-of-the-ordinary thing idea that it is hard to understand, or deserves to be challenged?
And what about moving cameras? At my age, my days of handholding at 1/30th sec are over. Even at 1/60th I have seen some motion blur in some of my shots. So I consider 1/125th to be my floor, and for a generous safety margin, I prefer 1/250th. Yes, I do have a tripod, and no, I'm not going to carry it around all the time.
As for apertures, unless the scene requires something else, I prefer f/8 (or there abouts). My lenses perform well around f/8. And f/8 gives me enough depth-of-field to allow for slight focusing errors. Again, I don't believe my preference for shooting around f/8 is unusual, or something I should have to defend.
I do use f/5.6 or wider when the subject benefits from the reduced depth of field, but I want that to be my choice, and not something imposed on me by an EI of 80 or 100. Likewise, I don't want to be forced to use f/13 or f/16 by an EI of 250 or greater. Sure, I can always put on a filter (I carry yellow, orange, polarizer, and ND filters). But when my meter at 250 keeps coming up f/11 and f/13, I got the idea that maybe I should look for a film I can shoot at EI 160-200.
But after reading some of the replies I am getting on Photrio, I guess that must have been a pretty crazy idea. :-(