Multiple stable 2.5amp sources for a Pi and other devices is important and not always reliable with many 12v->5v converters or even with (how I would probably do it) with a power bank that acts as a buffer and is charged via 12v.

It's messy but it works, if that bothers you then you should read about how inefficient compilers can be.

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.

it's not efficient, but who cares? using the bricks that come with your equipment and parts you can get at the hardware store solves problems quickly