It's still there but there hasn't been a need for a protocol to really use it. Protocols like HTTP(S) could really use the SCTP benefits but those need solid client implementations; server protocols like DNS or FTP are restricted more by their own limitations than by TCP, really. Of course you'll find niche use cases where SCTP would've been a godsend, but without proper Windows support _and_ broken middleboxes ruining everybody's internet experience, SCTP was sort of doomed from the start.
MPTCP has some compatibility advantages and TCP-inside-TCP allows for solid client side implementations that can be linked to the userland code itself (https://github.com/ngi-mptcp/curl/wiki/Multipath-TCP-on-Wind...) without elevating credentials; sadly, SCTP didn't have that luxury, as Windows (rightfully) restricted access to raw sockets not long after SCTP began to gain popularity among its fringe group of supporters.