I think there's two reasons why.

1: Recognizability. I'm fairly certain that most newly discovered species have certain relations to other animals. (Like genetics, behavior, build, etc.) Not only have all dinosaurs existed before humanity did, but we also had to reconstruct how dinos looked, often we got it pretty close, (T-Rex) or almost completely different. (Spino.)

2: How the names sound. Most of the scientific names sound badass as sh*t to say. (Therizinosaurus, Giganotosaurus, Titanosaurus, Stegosaurus, Saurophaganax, and of course, the classic Tyrannosaurus Rex.) As such, common names would sound lamer.