With my Doctor's emphatic blessing (don't ask) I have returned to tobacco after a 16-year pause. Back then, it was cigarettes and the occasional $10 cigar. Dry was something to be avoided. They sold me expensive wood boxes to ensure my cigars wouldn't be dry. I now gather the mention of pipe tobacco in a humidor would get me banished. So, why humidified cigars and not humidified pipe tobacco?
Hey, welcome (back)!
Moisture content is of course important for both.
It might be useful to think about the question in terms of stability and evenness. I think some parallels can be drawn
We let our Pipe tobacco age in tins or jars. Very stable (hopefully, no pinhole, bad seal, etc.). Zero (or very close to zero) air exchange with "the outside world. " Similar, people will take an unopened box of cigars and put it in a cooler for years. Sure, they'll use humi packs or whatever, but they deplete very slowly. Very stable, little air exchange, although more so than a sealed tin or jar (cooler opened periodically, etc.).
We open that tin of pipe tobacco and let it breathe (destabilize). It changes as we smoke the container down. Maybe we dry it a bit on purpose. But the pieces remain relatively stable (as moisture declines, however fast) because they are small.
Breathe time can be important. People sometimes say they didn't like a blend, jarred it for X, came back to it and "wow." This is why. Air exchange destabilized the environment, and evenness of moisture content is basically a non-issue. Same reason many feel that the best few smokes come from the end of the tin
Cigars too can benefit from breathe time. I buy a fiver, pull the cellos, and into the box they go for ?? time. Box is unstable (relative to a sealed tin), open, shut, drafty... guys with airtight Tupperware etc. should open them periodically. What we are looking for here is even moisture content, all the way through. Achieved by managing humidity in an environment with some air exchange over months, while your cigars both open up and settle in to a stable moisture content all the way through. This takes way more time than shreds of pipe tobacco
At the end of the day, your open tin or jar is slowly drying down, but it doesn't really matter. You're smoking away at it, it's mostly even, and will likely be gone before it's too dry. If we held a cigar in a non-humidified environment, not only would it slowly dry down, but it would be doing so unevenly. And we don't smoke them bit by bit... ("dryboxing" = the art of doing this on purpose and "catching" the cigar at just the right time for your conditions and preference)
Exceptions abound (of course), but hopefully these ideas add to your enjoyment