Ancestor worship is only useless if you only have sh-t ancestors.
Indo europeans of every branch have an awesome collection of ancestors to choose from in every single tradition both historical and mythological. I mean it’s an absurdly vast portfolio.
There is a reason the sh-tholes don’t practice ancestor worship, we did, china does in its own way, and japan still explicitly does: they don’t have any worthy of it.
Then we have the (((People))) who make them up or appropriate them from others, because they don’t have any ancestors worthy of worship either.
On the other hand, most of us whose ancestors built civilizations have many many many ancestors, and heroes to choose from.
The purpose of doing so is to continue the intergenerational contract. The sacred.