Why would you want to lower the price of a market in which you actively participate?
Do you not like making more gold $!?

There's a finite amount of gold you can spend in WoW, but there's an infinite amount of satisfaction in winning AH PvP.

@honky

I make more gold overall; much like Basil has stated below. I could squeeze out a bit more profit if I really wanted to, but I'm satisfied at my returns.

@Keith

You are 100% correct. Nothing is more enjoyable than kicking the butts of other greedy individuals.

@Basil

Yes sir. People are hesitant to spend 300g on a glyph, but will not balk at spending 100g or even 200g. So when you sell 10 glyphs at 100g vs two glyphs at 300g, your putting extra money into your pocket, especially if you corner the herb and ink market. If you item doesn't sell, then it's not worth as much =P

The flip side of dropping prices in an attempt to increase sales is that our expenses also multiply by the same number of sales. Instead of making 270g profit per glyph, we're now making 70g per glyph, so we need 4 times as many sales just to break even. It's a slippery slope that can rapidly fall to a price that requires infinite sales for zero profit. (My competition has this one all figured out.) No matter what the price, there's also a limited number of buyers on any given day - it's quite possible that sales won't reach the numbers we need to break even.

By increasing the number of required sales, we've also greatly increased the amount of time needed to support those sales. Instead of spending one hour milling and crafting and organizing and posting and canceling, we're now spending four hours just to make the same amount of gold (if not less). We're probably going to need to spend even more camping the AH to get that bottom spot on the list multiple times over of the course of the day instead of just taking that 3am sale to a desperate Australian. This is all time that could be spent pursuing other professions, skimming an hour's worth of the most profitable crafts from each of them to greatly increase the daily gold numbers (or, you know, actually playing the game).

@Zam

That is the downside for sure. If you don't plan out your actions beforehand, your going to be doing a lot of work to simply keep up with it.

Hence why this isn't usually the most recommended path to take when trying to make a lot of money.