after gaining 100 % warscore AI refuse to give up their land?

[Wizzington]

Points aren't the only factor by any means - I was able to force a 480-point vassalization on England with a warscore of 61%, even though they wouldn't accept ~70 points worth of ceded provinces.

The AI really hates giving up land and will hold on to as much of it as possible.

My experience is that if you occupy all their territory and have thoroughly routed their armies you can get peace settlements well in excess of 100 points. The status of their armies seems to play a key role for the AI in peace settlements in EUIII I've found.

Once I only controlled Turkey's European provinces, but after I finally cornered and destroyed their main army in Naxos, they were quite compliant despite a 50% warscore. In another instance, I had lots of provinces in hand and a higher warscore, but hadn't faced their main army yet and so it was still intact. They didn't want to give me squat, which sucked because I wasn't able to smash that monster and its powerful general.

War weariness and war capability are massive factors in getting a good peace settlement.

 

[Wizzington]

Different countries seems to react differently to peace offers. I had 100% against Hungary and 100% against Poland - Hungary accepted a peace deal worth nearly 200 whereas Poland was turning down anything above 90. Possibly this was because Poland still had allies (vassals and Lithuania) but my side had 100% against all of them as well.

Hungary probably had higher war weariness or they were out of manpower, etc.