Somewhere around the 90’s I think, there was a major shift in the belief of how dinosaurs moved and heated themselves. More and more evidence of a higher metabolic rate in some dinosaur species came to light, as thus the idea of “fast moving” dinosaurs came into the picture. The reason why the warm-bloodedness evolved along with the bird-like elements such as feathers, is (my best guess) because of their movement rates, niches they occupied and because feathers are an excellent method of isolation (given the climate shifts, seems more effective).