decades ago,why is the Mayan temple abandoned by its inhabitants?

Answer 1

It is not known for certain but many theories have been suggested.

1. War -- The cities were abandoned when they were defeated in a war either with other Maya or with some other group such as the Toltecs.

2. Disease -- Communicable diseases spread quickly amongst the densely packed inhabitants and the survivors fled.

3. Famine -- Over farming produced famine which lead to widespread starvation, people fled to find better farm land.

4. Bad Omens -- The Maya were obsessed with time and prophecy perhaps a bad omen told them it was time to leave.

Of course not all of the Maya cities were abandoned. Some of them were still inhabitated until the Spanish arrived.

Answer 2

Current thought now is a combination of warfare, drought, and deforesting. (They cut down all the trees to burn to make lime paste to paint all the buildings white.) The cities could no longer support large groups of people so they dispersed into smaller groups.
The Maya had left their cities long before the Spanish came, contrary to what Mel Gibson's recent movie claimed.

Answer 3

No one knows for sure why this happened.