The empress is suffering bcs of her father that piece of shit

But at least he's regretful. Does that make him less of a piece of sh*t? No. But if he really regrets it, he knows that it's wrong and he made a mistake.

(Also it makes him easier to manipulate when MC's family needs to kill off the basturd emperor later, since her daughter's freedom is at sake.)

It's not a mistake, what he did is not a mistake it's his decision, he's not being regretful at all