Why were paintings during the Renaissance mostly religious, e.g., Jesus and his crucifixion?

Most, if not all of the most famous Renaissance-era religious paintings were commissioned by royal and political figures; Christian themed artwork, in particular, was popular among these high-ranking and influential figures because they almost always included artistic representations of the royal and or political figures themselves in them which in many respects deified them. For example, in Jean Fouquet’s c. 1470 miniature entitled, “Christ before Pilate,” which was commissioned by Étienne Chevalier, treasurer to King Charles VII of France, Jesus is standing in what looks like a traditional French throne room, and he is standing before a figure that resembles the King of France; furthermore, Jesus is surrounded by soldiers that look like French cavalrymen. There is a robed figure in the room that resembles the treasurer to the king, and there is a clerical figure in the room that resembles the Pope of the Catholic Church. Now it goes without saying that this is not what the biblical scene actually looked like having taken place in Jerusalem in A.D. 34, but the painting having been crafted by Fouquet in a way that resembled French dignitaries, was surely flattering, and no doubt a worthwhile work for any French royal figure to commission.

This image is Jean Fouquet’s c. 1470 miniature entitled, “Christ before Pilate.”

https://qph.fs.quoracdn.net/main-qimg-17247529874c21f84354777ad3f43529.webp