Let's take a nice old "dry" block of briar.
Let's punch a big hole in it.
What this picture shows is a little ring of moisture at the top of the block - being driven out by the heat of the drilling process. That moisture is sitting in every block unless the block has been stored on the moon. Ambient moisture, the air is full of it, every wooden object is too.
Every time you heat up a pipe by smoking it, you drive a little moisture out. This is the pressure that blisters a cheap finish. But a thin coat of shellac does nothing to prevent this moisture from being pushed out. And hell, you could probably coat a pipe with Tremclad and it would smoke fine. We aren't talking about water needing to gush out the sides of a pipe, we are talking about a little bit of moisture trying to escape, which it can probably do out the chamber-side anyhow if it wanted. And a well-smoked pipe probably has less moisture content to start with, if a guy is driving it out pretty frequent.
Bad smoking pipes smoke bad for any number of reasons. Usually it's the geometry of the stem and bad drilling. But bad briar (or things that may not be briar), unnecessary metal gizmos, poor build quality... all leads to a bad smoking pipe. The result is that someone buys a 20 dollar pipe, it smokes awful, the finish peels off, and they say "Ah, this is a terrible pipe because of the finish" The might as well deduce that it's terrible because it's brown.
Anyone on this board who is smoking a rusticated or sandblasted pipe is smoking a pipe that has a hard finish on it. The seem to smoke fine.