[zkms]

This is a data-acquisition tool made by academics that lives in an environment (hybrid passenger automobile) where some extra weight and some conversion loss is utterly fine.

What matters here is reliability -- the device runs without being attended, and needs to keep working otherwise data gets lost / doesn't get collected. These researchers don't really have the inclination to faff around with designing a DC-DC converter system, they're trying to study IMSI catchers!

Were this to be made an actual polished product or deployed in an environment (like in a UAV) where weight/loss matters, I'm sure that someone could design a DC-DC conversion system that's tolerant of the nasty transients on automobile 12V bus and also supplies all needed voltages, without any needless conversions.