I was making some for a while, but I think the hard part is coming up with new ideas for pictures, and also not getting fatigued from looking through hundreds of similar pictures and thinking "is this one the best? Or is this other one sliiightly better?"
You can still make them! Even on your own if you have a moderately good PC.
It's just that it's kinda useless, and finding a good image for the background is hard. You need something the AI can use to set the brightness, but no matter if it's bright or dark it must still be recognizable as part of the background image. So the image needs to be something without overarching structure. But you need overarching structure to fool the viewer into believing it's just a normal image.
A reference to Habbakuk 3:11 in the Bible, which Jesus alludes to in his triumphal entrance into Jerusalem (see Luke 19:40). Habbakuk is prophesying against the people of God and saying they've become such a bunch of self-serving hypocrites that even the stones and timbers of their house (figurative or literal) cry out against them.
If you want more explanation, I'm happy to unpack it more, but that's where it comes from.
As to why someone felt it made a good message for a rock wall? I don't know. Often Christians interpret it as the stones are crying out in joy at Jesus' arrival, but that misses the Habakkuk allusion, the political reality of Jesus' conflict with the Jerusalem temple authorities, and the context in which "hosanna" historically gets used.
For some reason, I thought of Reverend Dexter from Babylon 5
"Every day, here and at home, we are warned about the enemy. But who is the enemy? Is it the alien? Well, we are all alien to one another. Is it the one who believes differently than we do? No, not at all, my friends. The enemy is fear. The enemy is ignorance. The enemy is the one who tells you that you must hate that which is different. Because, in the end, that hate will turn on you. And that same hate will destroy you.", followed by the hymn
It still hits me hard, one of the best juxtaposition scenes in a series. Chilling and beautiful.