Are you saying that vertical, bare bulbs are illegal?
I can't speak with any authority, but they probably are in some locales because of existing fire code.
That's not about growers per se, but about fixture types in industrial settings. The same applies to using UL rated hardware. Combine that with an official aversion to caregiver ops, and, well, there you are.
I suspect that the City & County of Denver is perhaps more lenient than many of the 'burbs.