From what I recall, one downside to SCTP is that things like resuming from different IP addresses and arbitrarily changing the amount of connections per socket didn't work well in standard SCTP. Plus the TLS story isn't as easy. QUIC makes that stuff easier to work with from an application perspective.

Still a fascinating protocol, doomed to be used exclusively as a weird middle layer for websockets and as a carrier protocol for internal telco networks.