Deloria jr writes about it in God is Red, but its essentially them trying to steal a connection to the Land.

It seems to be a thing all colonisers do: until Gaul was safe for the Romans and the native culture wiped out Roman hated gallic culture and druids especially; once the native culture was crushed and nonthreatening to Roman rule, you see roman settlers start claiming their great granpa was a druid or a celtic princess or whatever bullshit