Think about it for a sec. Steel or aluminium is going to yield a hell of a lot quicker than titanium. If you try to bend a phone those materials are going to yield before the glass. All the energy is going to break the frame then the adhesive of the glass from the frame.
Titanium frame? Glass will yield before the frame. There's no strain relief that the frame provides by sacrificing itself. It'll withstand more force but the glass now has the lowest strength.
"Given its strength, titanium is remarkably light. When compared to steel in a strength-to-weight ratio, titanium is far superior. The metal is as strong as steel but remains 45% lighter. In fact, titanium has the highest strength-to-weight ratio of all known metals".
And if you see the test, the titanium skeleton doesn't break at all on the bending test, it's the glass part that breaks only.
So, if the steel frame wasn't a problem stength wise, the titanium should be one either is my point.
Because I felt like the parent's comment "The previous iPhone used a steel frame. The titanium makes it lighter, not stronger" was about how titanium is at fault here (implied: weaker, not just "not stronger").
Titanium frame? Glass will yield before the frame. There's no strain relief that the frame provides by sacrificing itself. It'll withstand more force but the glass now has the lowest strength.