for the same reason people claim to get amazing yields from LED...most people do not understand lighting...most people think more is best...cant calculate lumens needed pure square foot...or know whats needed to cool certain lights. its all about recreating the sun indoors. and the sun contains a large amount of UVB rays. most lights put off little to none of best spectrum of total light....its not just about the light you can see with your eyes. HPS, MH, CFL, none of contain enough UVB to help trich production...a CMH light setup would cover all your needs...or can supplement other lighting with UVB reptile lights. most people think "just pack it with a ton of bright lights and thats all you need" which isnt the case. a lot of it comes down to research...half of the new growers come to this site and read 1/4 of a thread and take all they see as facts...if people would look outside the black market marijuana underground and research simple botany...they would learn a thousand times more info elsewhere.