From a political standpoint. Fate. My arse! All I see is a guy, that got chosen to save the kingdom. And that after he finished his business and did more then his part for king and country, he gets forced by said king and country to sacrifice the rest of his live. That's the epotome of un-thankfulness. So a lose hero, that might go to other countries, would make managing stuff for the nobles more difficult. How about, that's their job? A burning kingdom would be much worse, wouldn't it? I'm just surprised none of their precious heros turned against them.
As for the poor heros before....Would it have been too much to talk things out with her in her previous lives? They couldn't even be bothered to visit her in person and tell her it's over. I don't let the excuses pass, that they have been told they would kill her, lied to them, she got married or killed. They could have fought for her, confronted or even just looked if it's true at least once or visit their village and her grave, just to make sure. They didn't.
It's a different story, if they have been brainwashed or killed and replaced with a fake.
@Lumian: "I wouldn‘t ve surprised if the hero himself gets reincarnated time and time again as well. And he always remembers what he did to his first lover like she does."
If that's what happened, that guy should be beaten up for 3 lives worth. In that case there is no excuse left. He should have run off with her, as soon as he could or stay away from her.
@Dantrig: I wouldn't be surprised, if whole lives of her have been purged from her memories. Those in which she didn't turn evil, but followed the hero and try to hold on to him. The people turned against her and that's what she saw.