Soil in a rain forest is notoriously unfertile. The nutrients provided by decaying plants and animals get used up quickly by the fast-growing plants, leaving nothing left in the soil for additional growth. To solve that problem, the Mayans cut a new swath out of the jungle every couple of years and burned the old growth to provide nutrients to the soil. The new plot would provide decent crops for about three or four years before the nutrients had been leached out of the soil and the farmer was forced to cut a new field.
Because of the poor soil, it is estimated that there could never be more than about three families living in one square mile of land – the land could never support than that. Which means, of course, that they lived very spread out.
So what about these cities they are so famous for? The cities were religious centers only. Priests lived in the cities, and would carry out daily religious duties, particularly sacrifices. The peasants would periodically gather for religious ceremonies and festivals. For reasons that we don't understand the Mayans abandoned their cities around 900 AD.
Life for the majority of the Mayan people didn’t change much at all after the cities were abandoned. The peasant continued to work their fields. They continued to carve our new farms every few years. The only thing that changed for them was that they no longer made their periodic journeys to the cities.