You're assuming that "observing the Earth's atmosphere" is a yes/no question when it's actually a spectrum. I'm not familiar with the matter, but I can imagine

You're assuming that "observing the Earth's atmosphere" is a yes/no question when it's actually a spectrum. I'm not familiar with the matter, but I can imagine a scenario like "We need to record a very particular part of the EM spectrum and all those existing satellites happen not to have suitable equipment for that."