For "copter" style drones, 3D printing is basically a "noob" meme at this point; everyone thinks it's a good idea, tries it, and realizes that it's actually really hard and doesn't work.

Copter-style drones are exposed to vibration across a huge frequency range in every axis, and it's almost impossible to avoid really nasty resonance issues using generally-printable FDM filaments and "standard" design techniques; it's a lot easier to just use super-stiff carbon fiber and CNC it.

For planes, like what you linked, 3D printing is more "plausible" than for copters but also not really practical; you can 3D print a good plane, but plastic lacks the durability and favorable weight characteristics of foam - plastic planes tend to be "one time crashed" while foam is easy to repair, restore, and rebuild.

Stiffness. Important for how the frame behaves under load and buffetting etc.