its not a story, HMX has the DLC releases lined up for at LEAST the next 6 months, and they've specifically told Noble we can't go after certain bands because "we plan to go after them in the future", Loopychew explained it perfectly, HMX simply does not have enough resources to release everything the community wants them to. The RBN has already released over 1,750 songs that would never have been released through HMX.
With HMX's limited resources, (everyone should have noticed this trend by now), they've been going after huge older bands and modern bands that are extremely popular, with at least a #1 single being released almost every week. The small profit margin from the RBN just isn't appealing to the bigger bands and companies since they typically have to spend a significant amount of money to get the stems ready for the RBN authors to work with, which can wipe out most of their profit margin.
With that, a LOT of bands end up getting passed aside by HMX and aren't interested in the RBN, this whole initiative is to target those bands to make the community happy. (and to try to bring more life into the RBN, or make more people aware of its existence)