I think the main issue with wisdom saves as the baseline is that a monster's wisdom takes no account of their personality or purpose, so a trained soldier would be easier to intimidate than the wise old herbalist. It's very inelegant.Honestly, a Wisdom save should suffice for that sort of thing if needed.
Using the old morale score allows you be more situation specific. A cowardly goblin is more likely to run than a martial hobgoblin. I just think about rolling when a monster hits half hp, when a leader is killed, or when half their allies are killed. It would be nice to have a table rather than having to refer to previous editions.