Why dont people use these units with other bulbs?
Not a stupid question at all. A lot of people don't use them because they just aren't "handy" enough. To use those fixtures, one typically has to build a custom canopy to fit them in.
Second reason they aren't used is because most of those fixtures are for NO lights. Most reefs require at least VHO
fluorescent lighting at a minimum. Now if you were building a FO
system, they would be great!!
fixtures would be great for reefs, but again, you have to be a little "handy" with tools to make it look good. I guess you could just throw the lights on top of a glass hood but it would look like crap. I am all about making my aquarium look like a work of art and not a science experiment.