It was one of those situations where the internet was part of the lease, and the property owners got the MSP to provide for multiple companies on the site. Sadly I wasn't a customer of either Juniper or the MSP, and it wasn't something they ever actually claimed to support.
Juniper themselves stated in the manual that this base model device didn't support SCTP, though on ever other level it was faster, more capable and more featureful than the mid-range but much older device it replaced. The MSP didn't have a clue that we (or anyone else for that matter) used SCTP so missed the single footnote mention that the command to enable SCTP forwarding might not be available on some base-level devices.
In their defence, I'm not sure _I'd_ have thought to check if SCTP was supported and I had it running on my network. It works over the internet, it's basically IP, how could it not be suppo---oh.