I think it isn't as popular for a couple of reasons. I don't know a ton about the field, but I recently spoke to a pulmonologist. They essentially are trained as intensivists. I believe this is because if you are specializing in pulmonary care, then you will be a ventilator expert, and these are the people in the intensive care unit. They usually work in intensive care units, and often in specialty hospitals dealing with people with very difficult, chronic illnesses with poor outcomes. Of course this is not always the case, but usually it is; if you need a pulmonologist, you usually have a serious chronic problem. As a result of their having to be intensivists, their hours can stink. However, if you decide to work for a hospital in a community, and work where there are other intensivists, and don't need to make tons of money, you can swing working less hours. I think that it takes a certain type who enjoys that type of specialty.