There are plenty of foundations and the like though. The Schwartz Foundation funds a lot of neuroscience (particularly computational), but through grants to universities and researchers; Jerry Schwartz isn't really spending any time at the bench.
For basic research, this might make more sense. We know that, in principle, rockets can be built. Improving them isn't easy, but with enough time/money/effort, it can be done. For things like life extension, we don't know if it can be done, nor do we know the things we'd need to know to decide that (recuse as needed here). It'd be better to fund a broad portfolio of ideas than focus on your own enterprise.
It's also possible for these engineering-based companies to make money en route to their goal. Mars would be awesome, but there's money to be made in geosync or even low earth orbit too, which helps keep the business going. In contrast, there's no market for 1/3 of a possible antibiotic.
