Why Ancient?

If it's NOT ancient, then it's too easy to tell people that they just made it up.

Pop-culture Pagans and chaotes get that a lot.

Even modern religions based purely on personal gnosis, such as with the Otherfaith.

Of course, it could be that such an ancient religion was just made up from the beginning and people just stuck with it for a long time for no reason, but there remains some sense of authority in ancientness.

Many beliefs are generally believed "because they are ancient" because the individual has chosen to believe in them. This is done for that person's own reasons.

For instance, I might pray to Selene when I see a beautiful moonlight night, because I believe she does exist in some fashion. Whether that be as a deity, as a thoughtform/godform, an archetype, or as anything else doesn't matter so much to me as that I have chosen to believe she does exist.

But believing Selene exists has nothing to do with understanding all there is to know about the moon nor does it have anything to do with walking on the moon. If Selene indicates she feels that either can be used to worship/honor then so be it.

But an eye should always be kept on the past and how things were done before because without a foundation you have no building.

Very true. Most "modern" pagans think that just because it is ancient it is gospel. They must remember that witchcraft is the predecessor to modern science and medicine and should respect the advances that they have made. The craft merely offers alternatives.