This was such a hard problem for us to solve. I really liked the idea of track-pack subscriptions, and Apple was excited that we were willing to try out the new subscription option for the Games category, but there just wasn't a perfect way to present them.
For instance, if we included all previous tracks to new subscribers, it didn't seem fair to those who had paid for them previously. We've talked about introducing old track packs as standard in-app purchases, and still may do that.
There were other challenges too, based around some parameters on iOS, and I think we probably arrived at the best approach, all things considered.
Glad you like the feature!