Uh, that's one possibility. The other possibility is that they're studying something they're truly passionate about, and they aren't focused on how - exactly - the're going to make a living.
I know a number of folks who simply fed their curiosity, and still ended up in productive lives. Indeed, the original purpose of an undergraduate degree was to expand one's horizons. Graduate school was the time and place to focus on profession.
The folks you know wouldn't happen to be over 35 or independently wealthy, would they? Tuitions have gone up tremendously in recent years, and following your bliss like it was 1998 would be a disaster now if you didn't have a good job lined up at the end, or at least a trust fund.
I know a number of folks who simply fed their curiosity, and still ended up in productive lives. Indeed, the original purpose of an undergraduate degree was to expand one's horizons. Graduate school was the time and place to focus on profession.