There's a difference between inculturation and syncretism. It is one thing to incorporate into Christianity a non-religious cultural element, it's another to accept a religious element per se. In the case of the Pantheon, Christianity was wholly substituted for Pagan worship. Only the building was retained, a religiously neutral artifact. So too with the sites of springs or the dates of feasts, all were religiously neutral. But a PRAYER or HYMN to a false god IS religious--it is syncretic and heretical.
Smearing a forehead with ashes and giving flowers doesn't involve any prayers or hymns to false Gods. And of course, the prayers and hymns could also be reworded to be directed towards the Lord.