Why do Christians worship a god invented 3k years ago and not one invented 200k years ago?
YHWH is probably very old. He would have been one of the many gods in a middle eastern pantheon whose origin is lost in antquity.
It was the custom for each tribe or city-state to have its own 'patron' god selected from this pantheon - the Canaanites had baal, the babylonians had marduk etc. YHWH ws the patron god of the Hebrew. That is the Hebrews believed YHWH was one god amongst many, but it was YHWH who protected them, in exchange for exclusive worship.
At least that was the view of the Hebrew's priests of YHWH! The Hebrew people do not seem to have been solid,unwavering YHWHists. Nor did all their kings. The (largely fictitious) history of the Hebrews in the OT is a cycle of disasters befalling the Hebrew as punishment for apostasy, often in the form of military defeat. Then a messianic figures comes forward who restores YHWHism and the Hebrews start to win battles again, until the next disaster.
About 3000 years ago (C7th bce) after a terrible defeat at the hands of the babylonians, the exiled priests of YHWH set about writing down all the old legends of the hebrew, nturally with YHWH in thes starring role!
So YHWH wasn't invented 3000 years ago, but his character got set in stone (or written on scrolls) about then. but YHWH is much older than that - perhaps not quite 200,000 years old, but more than 3000.