One of the discussions that we usually have, when talking about categories, beyond the how of creation and organization of categories, is the why of creation of categories.
There are many here who focus on use of categories, and stickers too, without a strong argument on why certain categories should be created. The usual argument is that categories should be used for some genealogical purpose. A good example of this are cemetery categories. By categorizing profiles into specific categories, they can be searched to look for people who are related to other people.
But some categories seem to be used, not so much for genealogical purposes, but much like some stickers, as just a way of noting things that should be in the Biography. For example, some of the categories regarding an occupation seem to serve less a genealogical purpose then just biographical notation. See, for example, the category of Farmers. I can't really use this for genealogical purposes, like finding other related people. I can find other Farmers, for sure. But I would be better off using the FAN Club or Cluster genealogy to further my research.
So where does this leave Census categories?
While it could be argued that a Census category structure could be used to search for related people (as related people can sometimes be found near each other in a location). However, the only way to make this useful would be to create all levels of subcategories of Census records (each decade, each state, each county, each enumeration district), and to systematically add every person, to every relevant category. It would be a huge undertaking.
As Ros said, it would potentially contain millions of people. As Danielle said, location categories already group people. And we're not the Census Bureau. This is the reason for the hesitation to continue with creating and using these categories. It seems sufficient to put Census citations on profiles, use location categories if you want. It's my opinion only, but categories should be used sparingly.