an estimated 22 million Syrians had to leave because of the Syrian civil war
It has good soil and a mild climate.
Natural elements typically erode ancient ( and all ) buildings and structures overtime. That and an increasing amount of tourist attraction also doesn’t help the decaying... well everything. An article from the guardian supports this and even says that last year the EU threatened to remove the funding of the Great Pompeii Project which conserves and restores this ancient site.