I would imagine that trying to stop a lion doing what it wants to do, short of killing it, is actually quite difficult. Sad though it is for the lion cubs, it’s the way nature works. There are codes of ethics for wildlife photographers which specifically prohibit interfering with the animals.
And even more to the point, hand-raising the babies of large predators and then releasing them into the wild is not as easy as it might seem. Young lions stay with their mothers for a considerable period of time, where they learn to hunt and survive. It’s not an easy thing for humans to take on that role, and it requires enormous committments of time as well as dedication, a safe and approriate environment and humans skilled and able to take on the task. And even then there is no guarantee of success.
If you look up the work of Joy and George Adamson, Gareth Patterson or Arjan Singh, all of whom work/ed with big cats (Singh in India with tigers, the others in Africa with lions), you’ll read about how very difficult, heartbreaking and dangerous such work can be.
As an aside, a friend of mine stayed with George Adamson at his camp at Kora, and I don’t think I’ve ever been so jealous of someone else’s experience … it sounded like such an extraordinary adventure.