It's because many people simply look at values such as: xxx listed starting at xx g. And promptly undercut that price without bothering to take a closer look.
Also, not every AH works the same, there are different people playing the market on different realms.
In any case, there is no other point to it other than to artificially push inflation at a certain point of the day - TO BUY STOCK CHEAPLY. And then to sell at other times of the day at profit - whether it's the base mat or a product.
Just a handful of listings wouldn't do it, because as you rightly put it they would instantly be bought out and hence be irrelevant. Multiple pages of 1x per is how you actually do it.