In addition to Jack's points(shich were very good), I would also like to add a few:

1. Ease of care. A new keeper killing a pet within a few months is a big turnoff to some. Also, if a breeder sells a reptile to a person and that reptile dies because the care was too difficult, the chances that the person will be a repeat customer decreases. People like easy....Why do you think Crested Geckos have become so popular? Easy, Easy, Easy

2. Specialist. Most keepers avoid specialist. Some snakes are strictly lizard eaters, frog eaters, and egg eaters. People like animals that are easy to feed. You will never see Eastern Hognoses or vine snakes as a top pet snake. With lizards, horned lizards are a good example because they eat only harvester ants; yet the are some of the neatest creatures out there.

3. Cost. For both the consumer and the producer. This includes the cost of the initial animal purchase as well as vet care, housing, food, and husbandry equipment.

4. Incubation time. or 'quick turnover' if you look at it in business terms. Some species of lizards take almost a year to incubate the eggs. Not a couple of months like most snakes. Other eggs go through diapause and must be incubated at various tempeatures. If you had to wait a year for your ball python eggs to hatch how would that change your business?

That is just a few other factors that I think are part of the equation....and I am sure there are several more