Why do apples in every region taste differently?

I think it might be the quality of the water. For example I traveled a bit and noticed that cola tastes different from Edmonton and North Dakota.

Dirt makes a difference. Clay soil versus other soil. Acidity in the soil.

The other two answers are right. Just to add on to that, the water and soil nutrient contents of the region makes the plants to genetically adapt to it. So, even though we give it a homogenous scientific hybrid name, the taste (sometimes color, nutrient content, sugar content, etc,) will vary. The best flavor willl always be the fruit that is native to that particular region. If we take the same fruit and plant it in another region, it tastes different. Here in my country, such experiments were done on mangoes. They took the best tasting mangoes and tried to grow it in places that have richer soil. Despite the soil being rich, the hybrids ended up not tasting as good as the native place….So, they stopped doing it and in fact, our mango hybrids are actually named after the region in which they are grown!

The chemical and PH balance makeup of the soil, primarily, and the water.

There are also many different varietis of apples. Each has its own strengths and weaknesses.
I have an old orchard with ~50 apple trees. They are in bloom right now by the way. Beautiful

There are characteristics that make each variety of apple better for: cooking vs. eating, or long storage vs rich flavor, Tart vs sweet, flavor vs. texture, rapid oxidation vs sweetness, pest resistance, drought resistant, cold resistant vs heat tolerant, early maturation date vs late, etc. My red delicious apples mature in mid to late September. My golden delicious mature around 10/31. The Macintosh mature around 10/1.

Also new varieties come out every few years. Cornell Cooperative Extension is constantly tweaking apple varieties. I love Empire and Fujis now, but in 3 years there will, no doubt, be something even more awesome.

Honey Crisp Apple is the best. The University of Minnesota created it.

It has to do with everything. Soil, variety, climate conditions that particular year. Just like the Honey Crisp, they play around with creating new apples. Some apples are probably created to endure shipping, some sweeter, some brighter color, they play with all sort of things.