Given the license gives them complete freedom of what the do with FreeBSD, I wouldn't agree they have any duty. I would agree it would be nice, for sure it would be welcome, but nice & welcome doesn't constitute any duties. Just imagine under how huge pressure and scrutiny ALL linux distros, projects and companies should be for using OpenSSH _everywhere_ and not donating a penny to OpenSSH/OpenBSD projects. But the license allows it and that's the point and spirit of Open Source in eyes of BSD.