It's a deterrent to try and reduce the number of yukkuris bought to abuse, as constantly doing so would rack up bills as they have to be replaced; people keeping them as pets would be making far less purchases. For individual ones though, the price isn't quite as bad. Depends on what you want in your yukkuri (in both senses of that) and how much dedication and money you have. For example, the standard behaviour may be very appealing and usable to some.
Yeah basically it means "it cost more so you won't buy more to abuse them" non abusers won't get discount it just means that it would be costy to buy many and constantly to satisfy the abuser's need.
Besides, there always are those yukkuris produced specifically for Abuse, probably the point is "please we already have "for abuse" types, don't use this "for pet use" in abusive activity use the "for abuse" ones, thanks."