Because contrary to popular belief in these forums, it is actually possible to give plants exactly what they need without expensive concoctions..
Using high-end nutrients/soil/additives for dope is like painting by numbers or following a recipe.. If you're a noob grower who can't afford to mess up, then those idiot-proof regimen products are worth the extra money.. But trust Uncle Ben when he says he gets better results with his own mixes.. Every plant has a different appetite.. Learn the intricacies of that with the plants you're growing, and the sky is the limit..
I'd be REALLY intrigued if a nutrient product was released that claimed to be the perfect concoction for say thai sativas.. But no.. Apparently you can design a single perfect blend for every strain of one of the most diverse plants on the planet..
I prefer clones, and the reason being is that when every plant on your table is identical, its possible to work out a perfect regimen for all.. Every time I grew from seed was a new learning experience, and I had to tinker with individuals to keep them in peak condition..