For twenty years the story was clean: around 8000 BC the builders of Göbekli Tepe deliberately backfilled their own enclosures, decommissioning them, sealing the T-shaped pillars under rubble and feast debris. Klaus Schmidt, who led the excavation from 1995, read the fill that way and published it that way.
Post-2017 work by the German Archaeological Institute team revised it. The fill is not one event and not one process. Some is anthropogenic dumping. Some is slope slide — rain and earthquake moving material downhill over centuries, with rebuilding happening among the ruins in between.
The honest current answer is “deliberate, natural, or both, depending which part of the mound you are standing on.” That is less quotable than a ritual burial, and it is the position the excavators actually hold.
It is worth saying plainly, because roughly 5% of the mound has been excavated — a figure the dig team itself uses. Most of what will be said about Göbekli Tepe has not been found yet.