If you contributed a reasonable patch to Apache Mesos, implementing a feature like enhanced authentication, and then that patch was reject with such an excuse,

If you contributed a reasonable patch to Apache Mesos, implementing a feature like enhanced authentication, and then that patch was reject with such an excuse, that would be a problem. But Mesosphere choosing not to contribute specific features back is their choice. The long term belief in a healthy community is that enough people will contribute patches that make the project better.