We possibly have encountered graduate students with differing lifestyles, but a lot of the grad students I know in the natural sciences have grueling schedules between taking classes, TAing, and conducting research. The way these activities are structured may not correspond to a typical 9-5 but they’re still intense in their own right. To add onto this - attending conferences isn’t always on the universities dime, often it comes out of grants and other associated project costs that are allotted for your research. Maybe the university does foot the bill in other cases, but these are marginal costs when compared to the realizable value brought by graduate students in the form of monetizable knowledge and subsidized teaching costs. The latter point is at the crux of most tension between graduate students and university administrations, and there’s a large imbalance between the tangible value that grad students (and most academic researchers) bring to universities and the way that they’re compensated.