The reason there are no modern top-breaks is simply that they are not as strong as revolvers with a solid top strap and they will eventually wear at the joint. And please no lectures about the British Webleys and how strong they are (the guns aren't strong - the ammo is weak).
In a modern revolver, the pressure pushes the case back against the breech face; that tends to try to stretch the top strap. The stronger the load, the more strain is put on the top strap. If the revolver is a top break, the joint tries to pull apart and the parts are subjected to some small amount of pounding. With each shot, the gap grows until eventually it becomes large enough that the gun won't close properly and is dangerous.
There is really no way around this. With a lot of hardened steel, wear could be delayed, but it would still occur if the ammo was hot enough. Further, the top latch itself would add complexity and cost to the product.
If anyone wants a top-break revolver, there are plenty around, including the British guns, which are very decent quality within their ammunition limitations. But if you want a top-break revolver firing .44 Magnum or even .357 Magnum, I think you will probably wait a long time.
Jim