Asexual propagation

I just bought some thornless blackberry vines for my backyard. The label states that asexual propagation (I assume cloning) is illegal for this specific plant.

Can anyone tell me why?

From this article on asexual propagation methods.

I don’t know if it varies regionally, but I thought that the propagation ban only covered propagation for resale/distribution and that the gardener was permitted to propagate for own use.

(it’s pretty near impossible to prevent a blackberry plant from propagating vegetatively).