In Australia we call this "skimpflation" because they aren't shrinking the final product, they're skimping on ingredients to lower production costs.
It's the bane of my existence because brands I know and love will change their ingredients without warning and without changing anything on the packaging (sometimes not even changing the ingredients list! If the ingredients list has always just said "starch" they don't have to change anything going from arrowroot starch to cheaper potato starch)
I have allergies and I've bought two boxes of the same product at the same time, and had an allergic reaction to one, but not the other.
I used to always blame it on my housemates not washing the cooking utensils properly, but I now use separate cooking equipment and I clean down the kitchen before I start and cook at odd times so I'm the only one using the kitchen.
I've started emailing companies after my allergic reactions to determine if they have changed an ingredient, and 90% of the time they confirm they have changed the ingredients. Usually they put some PR spin on it about the new ingredient being more allergy friendly or sustainable (they don't clarify "environmentally" so I assume they mean "financially sustainable for the profits of our company")
I also can't fathom how they stayed on the shelves after Vegemite was invented. It's the superior black toast tar.
And I'm not just saying that because I'm Australian and eat Vegemite off a spoon.
I was raised on Marmite, and promite, and I found them disgusting. Genuinely thought all the black yeast biproducts were the same, mum was of the opinion that "we have Vegemite at home" when what we had was Dick Smith's Ozemite.
Was introduced to name brand Vegemite in my late teens and finally understood why this product has survived capitalism. It's so fucking good.
I've never tried bovril (was raised vegetarian, and developed an alpha-gal allergy later in life), but I've definitely tried every application you can think of for Vegemite - it's good in gravy, including making a vegetarian "beef tea" and "Vegemite cordial" for hot days.