But it wasn't always that way.
Margarine, as originally invented, is an emulsification of skim milk and tallow. Yes tallow, the ultimate perfect fat (when from grass finished beef) in my diet plan. I regularly render large amounts of tallow and then it just sits there unless I want to do some deep fat frying, because it's too hard to easily spoon out for everyday cooking.
Making margarine from tallow would be a great way to serve more tallow, and there are options for making dairy free margarine for those allergic to dairy and looking for a decent spread or soft cooking fat.
Andreas Viestad suggests limitless possibilities with emulsification of fats and labels them all margarine. You could use tallow, coconut oil, coconut water, brightly colored juices, etc...
This vegan recipe describes well the emulsification process, using the freezer to cool the fat quickly while emulsified.
denisedaniel concocted a recipe using tallow/lard and cashew milk to get around major allergy problems.
Lost Formula has bulk recipes for margarine. (From 1927? Possibly a rough translation.) That include several different fat alternatives and are flavored with a bit of cream.
The Washington Post has a couple additional recipes:
I think this is going to become an experiment soon in my kitchen.