In Jesus' time both Greeks and Romans who ruled Judea where Jesus lived had many Gods

"Eloi" is a plural noun for God which means he was saying "GODS" and not just singular GOD and the reason for this I could easily suppose is that you are dealing with Romans ruling you then. Then under that you have the Jewish Church and Jewish King Herod who has just executed Jesus' Cousin John the Baptist for preaching and baptizing people in the river there.

So, you have many different religions there from the Jewish religion to the Roman religion which is basically the same as the Greek Religion and both have multiple Gods. I think I cannot say that the Greek Religion and the Roman religion were the same religion but maybe different versions of the same thing sort of like Protestant and Catholics are basically the same religion. So, the Roman religion was more like Protestantism and the Greek Religion in this context would be more like the Catholic Religion or the religion from where the Roman religion began (even though the Roman Gods had different names than the Greek Gods they all were basically the same Gods doing similar things then too.

So, it makes sense that Jesus would use a plural Noun for God "Eloi" which often is thought of possibly then too as either 7 or 9 Gods like the candles of the Jewish Religion today.

The mix of religions was completely different then so the entire worldview of the average person in Judea then would be completely different than now. Also, mostly only kings were very highly educated in any language or religion or writing for the most part and even though Jesus was a trained Carpenter he was also educated somehow too along the way.

So, the fact that Jesus spoke "Eloi! Eloi!" makes completely sense to me in this cultural context especially after studying comparative religions since my 20s at this point.

What I discovered regarding all religions including shamanic ones before growing food was started is that most of these religions are mostly about what to eat, what to wear, how to behave around women and each other and how not to kill each other and how to take care of each other.

In other words all religions (almost without exception) are the basis of civilizations either large ones or the civilizing of the tribes people were members of by blood or adoption all the way back through recorded and prerecorded history.