Human beings evolved over the centures getting more and more refined in their food and lifestyle.
Processed food overtook the Raw food, hence, wisdom teeth or the last teeth weren’t required to serve the function of chewing to that extent. Also, over the centuries the size of the jaws are getting smaller which can easily accommodate 28 teeth but not the wisdom teeth in all the people.
This is the reason why, they don’t find enough space to erupt in the mouth and in some patients they are even inherently absent.