My guess is that you are on some sort of internal waiting list, since most of those programs have already made their decisions. They may have had several people turn them down for other REUs and are now looking to their next tier of applicants and checking which of those are available. Though, we also had one program that was keeping students in suspense past the notification date because we got so many good applications, they were scrambling to see if we could come up with some additional funding to invite more applicants than originally planned, so didn't want to make any decisions until they knew how many additional slots they could offer, and in the end, the money fell through anyway, so all that waiting was for nothing. Hopefully that doesn't happen to you.
Don't forget, even if you don't get accepted to an REU program, you can still contact faculty at local universities to see if they have an open position for a student worker for the summer, so you can still get experience, even if it might include more grunt work than an REU.
