Mainly, I don't want to race to get code ready for the once-per-year release, and I don't want to wait for an entire year if the code is not ready before the deadline.
Release any time a sufficiently important feature is ready and do not let any schedule pressure force you to compromise on quality.
Support the last two (or however many you want) releases, with support window dictated by the release process, relatively unpredictable but still reasonably acceptable for those of us who build from source.
Once in a while, tag a release LTS and support it for a period that makes distributors happy (four years?). That once in a while could be narrowed down as "once every half of the defined LTS support period" to make sure that you do not have to support more than four releases total, keeping the support obligation the same as today. It could also be synchronized with the timing of your major distributors to match their schedules.
Yuv's 2 cents
