First, the investment in liquid plastic and dye colors are more than most realize in order to be able to offer many colors. For light translucent colors, the more plastic is reheated / reused, the browner it becomes. Opaque dark colors are no problem but most anglers want lighter colors sometimes with flash flakes or white.
To be color-consistent requires exact amounts of dye added as well as flash flakes if ordered. Any customer would be right to complain about inconsistent lure colors different from those ordered in the past. I've even contacted Bass Pro and gotten lures sent at no charge for defective bags of lures that lacked metal flakes or were of a color too different from the catalog picture.
The degree of softness must also be consistent keeping in mind that some designs should not be too soft to have the right action.
Many molds don't have enough cavities to mass produce lures and therefore require a large investment in more molds which may not pay off in the long run if the lure design is no longer in demand. (Most multi-cavity aluminum molds cost over $100 each - especially injection molds that must be used to shoot lures with fine moving parts.)
Sell a few lures - fine, but on the whole not worth the time, expense, and at times - customer dissatisfaction. Cost-wise it doesn't pay for itself to make lures for personal use except I know I will never run out of a color or lure design I value, that will always be consistent in quality and tailor made for the conditions fished.
Plus it's not a bad winter activity waiting for the months to pass until the boat can be launched.