It may depend on the brands, but one big brand of mayo here in France (Amora) has all kinds of weird crap, apart from "whipped egg with lemon and oil".
It has rapeseed oil, which to me seems dubious since it requires special processing to make it non-toxic.
It only has 5.1% eggs (according to the label).
It also has "flavorings", thickeners and coloring agents.
So yeah, it's nothing like the homemade mayo I make, which only has olive oil, a bunch of eggs, mustard, and indeed some salt. Mine doesn't need any sort of coloring and is thick enough.