The correct answer is - fertile soil and pleasant climate.
The Central Plateau in Mexico has by far the biggest proportion of the population in this country. In general, it has always been the case historically that this is the part of the country that has been the most populated.
The reasons for this trend are very simple, fertile soil and pleasant climate. The Central Plateau has a very nice, deep, fertile soil, which is very productive and suitable for large scale production of crops, naturally that has attracted the people to live there. The climate too is pleasant, and unlike the tropical rainforest in the south and southeast of the country, or the deserts and semi-deserts in the northern part, this is by far the place with most suitable climate for the people to live in.