For Christianity (but not for other religions, or not necessarily) it seems that there may be a need for the Father, Son and Holy Ghost to be understood, depicted, discussed mostly in a concrete, personalized and simple fashion.
There are have been, at times, personalized depictions of God the Father - as an old man with a beard, most often (I think) but my impression is that since the mid-19th century this have dwindled and disappeared.
At the same time, the understanding and belief in God the Father has dwindled.
The Holy Ghost was seldom (I think) depicted as a man (but maybe as a dove) - however, His name has been changed from Ghost to Spirit - which is again a reduction in concreteness.
It is easy enough to believe in the reality of a ghost - but a spirit is imprecise and too vague to inspire love and worship.
The exception is Jesus Christ - who has continued to be depicted as a man - concretely (indeed, often enough depicted as only a man) - consequently (it seems to me) the strongest spirituality in the modern world relates very specifically to Jesus Christ and is hardly able even to discuss the Father or the Holy Ghost - and such discussions have a hollow and unconvincing ring to them - don't you think?
It seems only Jesus is really real to the modern Christian.
This is the secret of the relative success of evangelical denominations - the concrete reality of Jesus and therefore of a Jesus-focused Christianity; but focused almost exclusively and therefore - in practice - incomplete.
And for Catholics there is the Blessed Virgin Mary.
Much of her special power (in the Catholic denominations) comes (I believe) from the fact that she can be readily and un-forcedly understood and pictured and depicted as a sanctified human.
My point is that humans are as they are - which is focused on other humans at a very deep psychological level; on personal relationships; and this means that abstractions are not really-real to us (or, only to a very few) - and when the abstractions refer to God, and concrete representations are regarded as either wicked or dumb, then God becomes unreal - necessarily so.
Humans simply cannot, as a general rule, regard abstractions as real; cannot believe in abstractions - and, when we try to, we become confused and weakened by abstractions.
NOTE ADDED: In relation to abstraction and God, the disagreement between Christians - a 'disagreement' which amounts to a total inversion of assumptions hence perspective - is between those who regard God as too important to be abstract, and those who regard God as too important to be concrete.