The trinity is not a doctrinal issue in God’s word.
The Father, Son, and Spirit exist, but so what?
Other than the erroneous call in Acts regarding baptism that is found in later manuscripts, there is no trinity issue at all.
Perhaps catholics want to tie trinity to the pagan three finger pope salute?
Who knows.
Deuteronomy 13 says otherwise. We'll have to agree to disagree.