we do a bit of machining for planes and stuff…
modern steels are pretty strong, with really quite respectable strength-to-weight ratios.
the weight-savings offered by Titanium are often in the bits where you can’t hollow them out easily, usually through accessibility issues.
landing gear is a good example: great big lumps of metal, not all of which is easily hollow-able-out-able (actual aerospace terminology right there).
round tubes are already quite well optimised, there isn’t any un-stressed metal, so the weight savings aren’t as attractive as you might initially suspect.
it seems possible that Ti frames are pushed a little far, with high-strength alloys that may not be *ideal* for welding, in an attempt to squeeze out as much weight-saving as possible.
just my professional opinion guesswork, before i go home…