Black coffee and a latte are not the same product just because they both are coffee-based drinks. A latte doesn’t use brewed coffee at all, it uses espresso shots, and thus is mostly milk, not coffee. If you ordered a latte and got a cup of black coffee, that doesn’t even come close to what you ordered, unlike your hamburger/cheeseburger analogy where only the cheese of the difference

Either way, Starbucks does provide a non-dairy alternative for their latte however already: oat milk, almond milk, and soy milk, but they charge for those alternatives and that is where the issue is.

If they did not provide alternatives at all, or if they did not charge extra, there would be no issue. They either would have to remove the alternative options, which would reduce choice for everyone, or provide an alternative at no additional cost, which only eats into their massive profit margins a tiny bit. At wholesale bulk amounts like they buy, the cost difference is negligible for the product, and the markup on that substitution is insane.