Because the camera is likely to be larger, heavier, and festooned with additional dials, buttons and superfluous information. The only variables necessary for making an exposure are shutter speed and aperture, and the capacity to wind on the film. Everything beyond that hands some aspect of your photography to a technical designer. That's okay if you want your photography to be a collaboration rather than a personal decision, but I don't trust electronic engineers or software designers to know how I want my negative to come out, and experience has shown I'm correct to entertain that suspicion.
Film photography can be as complicated or a simple as you want to make it. Most film packets still have Sunny 16 info, and with a little experience even that will give you consistently exposed negatives. If your idea of fun is setting exposure bracketing for 1/2 or 1/3 stop increments, or spot metering for five different areas and letting the camera work out the average, you'll enjoy 1990s cameras. If you want street photography negatives that contain identical density, day after day and in all conditions, you shouldn't put your trust in automation.
Yes, my F100 is larger and heavier than my old FM2 was, yep more controls too, but it is also much easier to hold and adjust (even in manual mode) because of it's shape and the placement of the controls. I don't have to reach up on top of the camera to find the time wheel (my fingers are already where they need to be), and I don't have to stroke the advance lever (my fingers stay where they belong).
It is also has a much better meter in every mode, whether I'm using that to set the camera before the shoot or during.
When I finish a roll it automatically rewinds, pop the door and I'm ready to switch cassettes. When I load the film I pull the end of the film to the red dot, shut the camera, and push the shutter button. I don't have to roll the take-up reel to find the slot, then get the film in the slot, then roll the take-up reel, then shut the camera, then crank through the first 2-3 frames.
If I decide to switch films, the camera can (but doesn't have to) automatically set the ISO, this is really cool because if I grabbed a roll of FP4 by mistake in the dark when I was trying to grab a roll of D3200, or the opposite in the middle of a sunny day, at least the meter will give me data that is indexed to the film in the camera. The FM2 (like many older cameras) doesn't even have a window to let me see what I have in the camera.
Photography has a long history of automating tasks. Sheet film replaced poured plates, so we no longer had to make our own film. Roll film allowed us to advance the film rather than flip the holder. Automatic shutters allowed us to get past using a hat or cap hung on the lens to control time. There are hundreds of examples of things that have been automated.
The argument for using a camera without automation is an arbitrary and subjective decision about where to draw the line in time.
Automation is a good thing, so is learning to use dark slides as a shutter, pouring your own plates, and making carbon tissue.
I don't sense that you are suggesting we pour our own plates.