Got a rep on the phone, and he couldn't make it work. He said there was no "availability", that "they only make so many seats available." I said I thought JetBlue was revenue based, and that I could book the individual legs with points. I asked him to try the legs individually and he hung up on me.

Update:
Twitter Response: "You're correct, sorry about that! Those are both JetBlue flights so if you're not seeing it online any longer, it could be sold out. If you need help with your booking, you can always reach out to us through chat here:"

Flights are still available, however.

So, I go to online chat and get this:
JetBlue: I'm sorry but points booking has to be online only.
Then they insist I do it with a multi city search, however, the Use TrueBlue Points option is not available when you select multi-city.
Me: There is no option for a multicity trip using points
Me: Are you able to assist me?
JetBlue: I can't do the booking with points when you go to jetblue.com where you pick the option to be roundtrip ,oneway the next option is multi city you need to press that option
Me: Yes, I did that, but when you press multicity, the option for points booking disappears,
Me: Have you tried to do it yourself?
JetBlue: No because we don't do booking with points on our end, but yes I do multycity for customers paid with credit card
Me: Do you have a computer there?
Me: Go to jetblue.com and see if you can do a multicity booking with Points
JetBlue: Thanks for chatting with us! We’d love to hear your feedback. Please use the below link to provide your feedback.