For example, compare the Reese's Peanut Butter Cups to Trader Joe's peanut butter cups [0]. It may be that the Reese's ones used to use better chocolate or it may be that my tastes changed as I grew up. But I used to love them as kids and now they taste off. Similarly for Twix etc.
[0] I'm sure other stores sell peanut butter cups too. There's nothing special about the Trader Joe's ones other than they are mass produced and use better chocolate that Reese's.
EDIT: Flavor change may be due to cost-saving measures like replacing cocoa butter with vegetable oil https://www.today.com/food/chocoholics-sour-new-hersheys-for...
All stuff that's made in factories and needs to have shelf life, so I can only imagine it's any number of cost saving substitutions and preservatives and who knows what all for other reasons like preserving texture etc.
This happens to me too; I thought it was universal. I actually like it, though, for some reason (I guess the association with chocolate).
I have no idea why they use it, but I can think of one really good reason why they shouldn't, your product probably shouldn't have "hints of vomit" in its flavour profile.