Here are a couple of reasons:
If a. cue is not made yet, it's pretty hard to post a picture. Planning a limited run requires Some interest in advance. A proven track record, and an impeccable reputation facilitate the interest.
In a related vein, many/most pool players are gamblers. The idea of getting a good return on the initial investment is very appealing. The idea that the odds are greatly in your favor, is based on past track record and trust. There is also an added bonus in the excitement of not knowing how it will play out, and how big the payoff will be.
To degree, all cue purchases can contain some of these elements. Unless it is a pure collectible, you have no idea of the hit of the cue, which is the most important aspect. Pictures don't tell you that. That leaves you going back to the above, picture less aspects. You will need trust in the seller, and have to rely on the track record of the builder.