No company would create an entire park based on one IP, especially one they don't own. Even one they do own is a HUGE gamble.
Spending hundreds of millions on anything in a park is a risk, but if your park only has that one thing and something happens to taint the brand or it simply falls out of favor and you're stuck. If you have several IPs and one tanks, your park can still stay open and profitable while you retool the dud.
While Nintendo and Dreamworks may be key parts of a park, neither are worth a billion dollar+ gamble of its own park.