I think you are being a little hypercritical here. The format changes of the Discovery channels are not as frequent as one might think. At least no more frequent than any other major media company.
The Science channel never changed from its inception. It changed names from Discovery Science and Technology to Discovery Science to The Science Channel without changing its purpose. Of course now it should be called The Construction Channel.
The Military Channel was once Discovery Wings. One can say it just expanded its programming.
Discovery Health turning to OWN was a mistake.
BTW, "The Health Channel" was bought by Discovery Networks and folded into the already existing Discovery Health 7 or 8 years ago.
Investigation Discovery was Discovery Civilization. Discovery People was renamed from CBS Eye on People when it was purchased by the Discovery Networks. "People" rolled into the already existing Discovery Civilization.
The Travel Channel has been unchanged in purpose since its inception decades ago.
TLC was unchanged in purpose when purchased from an Appalachian educational group until much, much later. The main difference was that TLC began to show commercials. When the digital suite of channels took all the actual educational stuff, Discovery renamed "The Learning Channel" simply "TLC" and started the crap on there now.
The problem with Planet Green is that it was boring as hell, until recently anyway. The library was also fairly small so they had even more reruns than their sister channels (if that is even possible). Now that they have already started to re purpose programming from other genres they I have actually been watching it more and more, but not because of the "green" programming.