The moment we ask why, it has to have a reason. However Vedānta for example, would argue that brahman or the entity that is the cause of all causes, is causeless in itself. There can be no other explanation.

If something has a cause then it's ruled by cause and effect. If something is causeless, it not only does not need a reason to exist but is also the entity that puts forth cause and effect in motion. Kinda similar to Aristotle's concept of the prime mover.