The ad I keep seeing doesn't even hint at why Titanium matters. No matter, the point is, evidently the technical aspects don't seem to matter.
Titanium sounds cool, it sounds luxury, it's a marketing hack. Like <strike>"aircraft-grade"</strike> "space-grade" aluminum. Nobody is launching their aluminum phones at escape velocity. It's 100% for marketing reasons.
I have some titanium spoons, I feel into the trap too.
The previous iPhone Pro's have a stainless steel shell, not aluminum, and the ~30 gram difference is noticeable.
Of course, they caused this problem themselves by using stainless steel rather than aluminum like the regular iPhones, but they are nonetheless solving a problem with the titanium frame.