I noticed that in Diablo I they were everywhere: crosses on shrines, temple with crosses, crosses on graves; demonic pentagrams etc. Even the icon of the Holy Bolt spell.
In Diablo II, it was to a lesser degree, but still there, including the said icon.
In Diablo III, crosses are replaced with abstract symbols, and pentagrams with hexagrams.
Why do you think it happened? Were Zakarum symbols canceled when it became corrupted? ))