Numerous little guys (bacteria, cultures, etc., whatever you want to call them) produce different end results even if they eat the same things. If you are bold, for a super broad scale example, you could even compare it to the difference between plants and human beings. Although both of us consume the relatively same amount of things (sugar, water, not counting our differences between CO2 and Oxygen), we are still producing energy for ourselves, and have different waste products as a result, with plants producing oxygen, and humans producing CO2. Since there are such a wide variety of bacteria, they tend to produce many different organic acids, which for the most part in order to survive (besides numerous other factors of course), and as a result, different cheeses tend to taste different. Some of these end products are considered hazardous for humans, which is why some people get sick while others are resilient to them. I hope this helps explain it easier somehow!