Why is socionics the way it is?

[consentingadult]

IAny sources I find only describe what the system is, not why it is. ...How are the particular properties of the functions and elements explained and justified from the ground up?

They aren't. That's called Positivsm. Perfectly reasonable according to Auguste Comte.

[Nevero]

I've once heard an explanation that related four cognitive functions to four timespace dimensions but the arguments provided in proof were hopelessly trippy.