Why is it that pot pipes/bongs are rarely old-style wooden ones like the pipe sherlock holmes smoked?
Guessing that its because they need to be regularly cleaned of the sticky, gummy residue?
A wooden tobacco pipe is supposed to develop a “cake,” in other words the tobacco residue will line the inside of the bowl (a porous wooden surface) after having been smoked for a long time, and you want to leave it that way since it “breaks in” the pipe and makes the smoke richer each time it is smoked. After all, you smoke fine tobacco to savor the taste and smell of it.
Most people don’t smoke marijuana for the taste and smell. So you want a pipe that will provide you with a cool, non-abrasive smoke and will not alter the taste with gummed up resin in the bowl. You want to be able to clean the bowl easily, and the resin scrapes off the glass very easily since it’s a non porous surface. The best way to do it is to soak it in mouthwash or rubbing alcohol.
Not to mention that the bowl of a typical calabash pipe will hold about $50 worth of smoking material. Lots more than is needed, even if you are trying to turn on a whole team of cheerleaders. 
Ehhhh… from someone else’s experience…
When you use a wooden a bowl, and get desperate, you end up smoking wood.
It’s probably a combination of factors, but I think Eleusis identified the biggest of them; marijuana smoked in a pipe will not stay lit as readily as tobacco. The constant application of flame is too much for many (most? all?) wooden pipes.
Glass pipes, though fragile, are favored almost unanimously among pot smokers
Sherlock Holmes is mostly depicted as smoking a meerschaum {although in the stories he did use other pipes}, which isn’t wood: it’s a light and porous mineral somewhat akin to a denser pumice. It was frequently carved into elaborate shapes, and although initially light in colour, took on a darker tobacco hue with use and age: a dark meerschaum was regarded with pride by the owner as the badge of a seasoned smoker.