In her dissertation, Clare Rothschild argues that Hebrews is closely connected to the Pauline corpus and, in fact, never circulated independently of that corpus.
I would add that the very title of Hebrews -- Pros Hebraious -- was produced on the analogy with the other letters of Paul (Pros Romaious, Pros Philippesious, etc.). Therefore, both the title and the canonical position of Hebrews in the canon of the New Testament impies the name of Paul -- reasons I have argued that Hebrews is, in fact, Pauline. I have also tried to show that the internal evidence does not contradict this conclusion based on the external evidence.
We reject the Pauline authorship of Hebrews to our own loss.