I think (and I may be wrong) - he gets to write off the donation now (probably amortized) to help his tax basis even though the $ doesn't go anywhere until he's gone...
Yes, this is something I talked about with an estate attorney when we had kids and were setting up a living trust. Basically you can create an entity called a charitable trust which is a gift to a third party, that transfers on your death, and avoids estate taxes. What is more interesting is that many of these are more durable than language in one's will, specifically the will can be challenged and thrown out but a charitable trust won't get screwed because of it.
From the language I'd guess they might be setting up a charitable lead trust or gift annuity, where he'd actually be giving he money now but will continue to draw an income from it over the rest of his life. I'm fairly far removed at this point from a former career in university advancement though - that would certainly be much much larger than any I'd heard of before. There's probably also a fair chance he's already set up or is now setting up an independent foundation or trust that the money will reside in.
It's (I'd guess) fairly unlikely this is a standard bequest, though, given both the revokability and uncertain future tax status of that option. I imagine it would also take multiple years for an estate of that size to close and the funds to become available to CMU.
In terms of "why" of now, well, he gets to live for however much longer seeing his mom's name on a school that obviously means something to him, and as CMU is doing a big campaign, he gets to be a linchpin of that.