Please tell me if I'm wrong in this, but I'm assuming that you do not believe in evaluation, or any form of it. I don't mean any offense to you by that. Because if genetic information can only be lost, then how do you explain birds developing feathers in the first place? With evolution. Just how pre-modern Homo erectus changed when they migrated from Africa, conditions were different, and they adapted to their environment. You can't say that blue eyes came from the loss of brown, no, they were a genetic mutation, which is what evolution is.
And you ask why reptile grow feathers? Because that's not what I was saying they did, I said that they had feathers, not that they wanted then so they grew them. They developed feathers, and when the majority of life became extinct on earth, leaving the smallest, which included mammals, very small dinosaurs, reptiles and birds, that then evolved in the absence of large dinosaurs, that for many species, were their predators.
Oh, and I forgot to answer what you said about raptors. All fossils are different, and where they are geographic plays a large factor, because depending of climate, soil, etc., they will be preserved in varying levels of decomposition. Have you ever seen a decaying carcass? Or many, in my case, and some, especially the small, get covered very quickly by sentiment, plant matter, etc. Others, mostly the large ones, hang out for a long time, and by the time they are starting to be covered, only bones are left. Their are many factors.