Frumkin [from SocialEdge]:

Large private foundations do not seem to embrace this notion of scale as readily as individuals, though there are some notable exceptions to this. Picking any single nonprofit organization as the one that will be taken to scale may appear unfair and capricious. It implies that a single donor should be able to disturb the competitive landscape and decide who wins and loses in the nonprofit arena.  While this may be precisely what an individual would like to achieve, few foundations want to be perceived as inequitable and heavy-handed. As a consequence, they shy away from tipping the scales completely in favor of one organization over another. Moreover, foundations may be less likely to bring an organization to scale because their interests are not in the organizations they fund per se, but in the specific programs and outcomes which these organizations deliver.  The foundations have priorities that overlap somewhat with the agendas of nonprofit organizations. When these priorities change, funders can and do find new organizations.

Interesting points. When foundations really get the ownership bug, they do a Pew. In one way foundations are like venture capitalists [a tired metaphor, I'm aware]; they want to share the investment risk. I think foundations are becoming less reticent to "disturb the competitive landscape," and to let the nonprofit marketplace play itself out. I see fewer missions to rescue nonprofits [excluding those close to home and soul] that aren't performing. Frumkin's right, though, that foundations' priorities, as currently defined, don't involve helping their grantees grow strategically. That's unfortunate.