I feel that this kind of counter-question dodges the issue. Here is an example of the issue:
Even if I take away my 1% war score demand, the AI will refuse white peace. You'd think a nation that's been stackwiped multiple times might consider getting off scot free or with a very favorable deal (not that I'd allow that anyway, but still).
Just because length of war functions better than insta-peace doesn't mean that this mechanic is reasonable, and it definitely doesn't mean it's good. I think you can tune up the war goal as a stronger relative consideration, add factors like income/manpower as stronger considerations for the AI, and weight battles more (a nation losing lots of battles is not in good shape and should be looking for an out as war leader). So long as things work as now, the incentive for total war is overwhelming. It'd be nice for the player to actually weigh the pros and cons of extending the war for more gains as opposed to it being a false choice.
Asking obviously non-feasible counter questions isn't any more constructive than the opening post itself :/. At the end of the day, Portugal refusing to peace out for 1-5% war score even though it has a standing army of 2 regiments remaining suggests that the peace deals are due for at least some tuning...tuning we've seen way less often than AE changes or westernization changes despite that this particular mechanic is something a player will encounter in some form in nearly every game.
Edit: This also shows why the AI shouldn't be able to refuse stabhit offers, which are functionally designed as offers humans can't refuse for any real length of time. Rather than letting the AI get stabhit to high heck, it should just accept those.