I don't understand this point though, since on a yearly basis it will be roughly the same for them:

"This funding is sufficient to provide the Internet Society with broadly equivalent annual earnings we currently receive from PIR. And through responsible, well managed investment, we believe this fund will provide a comparable level of funding to the Internet Society in perpetuity."

So unless they were worried that .org was not as stable as an endowment, it seems like it didn't help them at all anyway. And this is at the cost of their core mission?