Asexual propagation

Factual Questions
1

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?

2

From this article on asexual propagation methods.

3

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).