Although there are libraries that run it over UDP, SCTP is really a genuine layer 4 protocol, which means that it needs to be implemented in the OS and supported by NAT gateways. QUIC is intended to always go over UDP, so it can be implemented in userland with easy updates.

SCTP deployment stalled when NAT boxes took over the internet. Also it was originally from the telco world and didn't have a lot of cheerleaders among internet applications people.

There's now an incarnation tunneled over UDP that's used in WebRTC. But tunneling rtp on dtls on sctp on udp sounds like a real protocol christmas tree...

Doing a SCTP four-way handshake and then a TLS handshake is going to be pretty high latency.

No MS support...