One of the main contributors to flavor comes from bacteria. When those bacteria die, they release all sorts of enzymes that break up the protein. The number of bacteria that you use as the acidifying culture makes a big difference. It helps to determine the extent of flavor development. The point in the bacteria's lifecycle at which you add rennet also matters. You want the bacteria to be past the lag phase. with DVI, 17 minutes is not long enough. It takes 45-60 minutes. Cooking the curd is about getting it to the right final texture, so that when you squeeze the curd in your hand, it should come together, but you should be able to separate it apart. I've never been able to get curd to that point in 15 mins. Too moist of a curd may lead to flavor defects, because as you're pressing it, too much whey is going out. But the curd in the middle when it releases whey, the whey can't escape well, so the liquid is trapped inside. Not a direct answer to why it tastes the same, though.
If you want different flavors, try using adjuncts to mimic non-starter lactic bacteria in milk. By these I mean thermophiles such as l helveticus. A small pinch of helveticus will help bring out sweet and nutty notes, and in cheeses like cheddar contributes a lot of aromatic compounds. They're present naturally in raw milk, it's part of why raw milk cheeses are better.
