There are many aquarium lighting companies that make these types of fixtures, because this intensity of lighting is exactly what people want to (and do) simulat

There are many aquarium lighting companies that make these types of fixtures, because this intensity of lighting is exactly what people want to (and do) simulate over their aquariums (though generally at spectrums that are bluer than daylight)! I think in terms of cost what the OP is not realizing is that when you are talking about hundreds of watts of LEDs, that is a lot of heat that is very concentrated. It takes a thoughtful design and active cooling to ensure the fixture is safe and the LEDs are kept at the proper temperates to maximize their life and performance. You don't really need to worry about active cooling when you have a few low wattage LED bulbs spread throughout a room. But cram a ton of them together in a small area and you absolutely do.