[mrkgnao]

Partly PR (like everything he does) and such unflattering things, but also partly an exercise of the ability (read "ubiquitous nerd dream" if you like) of thinking up outrageous solutions to pressing problems (e.g. inflatable "bouncy castle" air tunnel), which in this case differs from the usual in that said nerd is very rich (and also owns technology and employs people with skills appropriate to the problem) so the outrageous solution has some chance of actually being implemented in the real world

This differs from the option mentioned by someone else of "calling the right people" (perhaps by donating a chunk of money to send conventional rescue personnel/equipment) instead of flashily taking matters into his own hands: this is a display of ingenuity/out-of-the-box thinking/"a tunnel-making company that everyone says is a bad idea saved actual lives, see?" first (again, read something like "nerd saviourism" or a restricted form of "tech solutionism" if you like) and philanthropy second.

Similar idea to pushing his batteries in Puerto Rico, and also explains his lack of interest in Flint (often mentioned on Twitter) or similar humanitarian concerns, and hence his difference from a certain "philanthropic billionaire" stereotype exemplified by Gates and Buffett: he doesn't own a company that claims it can purify water in a way everyone thinks is either overpriced or stupid, so "those things would prove nothing". (A silly prediction along these lines: if there ever is some sort of emergency in the near future that requires transporting something very quickly from A to B, faster than a cargo airplane (and insert other wildly improbable things here), I'd expect him to offer to do the "NYC to Tokyo in 30 min" thing for free.)