Compared to NaCl, for someone who wants to learn how cryptography libraries work, "TLS" is too much of a moving target. It is unfinished software that may never be finished. Too many versions of too many libraries supporting too many ciphers by too many developers. Too many knobs and switches.

As for OpenSSL, not everyone is on 1.1 yet. There is no ChaCha20-Poly1305 in 1.0.1_. So while some bits of NaCl have been adopted into the TLS suite, it is only a subset of web servers that are supporting the so-called "subprotocol". And still no Ed25519, even though it has been used in OpenSSH for some time now.

All these factors make TLS undesirable for me. Too much complexity compared to NaCl, IMO. For others, TLS may be the right choice.