My take on this is our systems usually don't have as low a level of DOC in the ocean. We now pollution is a cause of bleaching along with other stress. We then add more radiance than is necessary for the corals' survival to the equation. The final leg of the equation would be temperature to throw the coral over the edge. The temperatures we keep the tanks at are most likely too high for the coral to deal with the stress from the DOC and light level. Light is getting the rap for the bleaching because we try to understand how it works but rarely can figure out enough to be confident. Add in more is better as a common disease of husbandry when it comes to light and we have our "culprit".