They are - there are all those mini effects that are basically the same as the full size effect but without a battery compartment, so they can be smaller. If you are making a pedalboard layout it makes sense. I prefer ones with batteries.
I agree at some point but there are some knobs that change something, but there is no real descriptive name for what it does. You have to call it something (or you could put a symbol on, but does that help?).
I think it is the other way round. Something becomes rare or unavailable, it then instantly becomes desirable. If those things were still made, there would be nothing like the same level of interest.
Plus there is the 'xx years old, must be better', where just because something is old it is desirable. Like people buying Kays!