Am I drinking "sparkling wine" or "champagne"? 
    Honestly, why should I care, I just care about 
    how much I like the product and how much it costs.

I think you are seriously underestimating the utility of walking into a store, seeing a product labeled as XYZ, and being assured that it meets some reasonable definition of XYZ without having to do a bunch of research and/or testing on your own.

Packaged food is an extremely cost-sensitive product category to put it mildly. There is tremendous pressure on these companies to shave off every penny they can when it comes to production costs.

I strongly suggest that we do not want to see what might happen if the FDA didn't enforce some kind of minimum definitions for various categories.

For a sneak peek of the probable outcome, you can learn about the history of adulterated food products: https://www.google.com/search?q=history+of+adulterated+food

I tend to agree with you but you might find this more common than you realize. I’ve noticed in my lifetime products I like change their recipes. I’ve also seen products once labeled as ice cream now labeled as frozen dairy dessert. I’ve seen this type of thing in lots of different products. Not just ice cream. And I’m not convinced anything changed legally in many cases. Usually I suspect it was to reduce costs.

It’s now something I actively look for on packaging when a product gets a new look.