I have an upcoming oral network security exam and know that in past exams, the professor asked about why TLS requires TCP. I know that there is DTLS but it wasn't part of the lecture. So the question is about what advantage TLS gains by requiring its underlying protocol to be TCP, I guess. I already heard some wild guesses but no convincing arguments.
At the lowest level, layered on top of some reliable transport protocol (e.g., TCP [TCP]), is the TLS Record Protocol.
Seemingly everywhere else (according to my judgment), the RFC doesn't only require "some reliable transport protocol" but TCP in particular.