My best guess is that the reason is purposeful from the beginning: to give customers what they want. Whether it is a good thing or not is irrelevant. I get about 30 people asking me each year if they can buy strawberry seed because plants are too "expensive".
Now I am getting more and more asking about buying lily seeds in commercial seed packets. Presently, I'd say it's up to ten people a year. The lily plugs, I believe, is attempt to satisfy the customer,
and make money.