Socionics is a model. It seeks to describe human relationships.
The simplest way to have a network of interacting nodes is to have each node have an "in", and an "out". (This is your ego block; the other 3 blocks are just ways of describing specific phenomena related to your specific "in" and "out"--they are logically superfluous and exist solely for clarity's sake.)
As for why there are 8 functions and not some other number, that is a Socionics history lesson I cannot administer.
etc etc can someone please finish this thought for me?
EDIT
That is a result of their abuse, not their use. The minute you use Socionics as a script is the minute you cross into abuse. I have not had this problem of abuse except in one situation. In all other respects Socionics has been a boon and helped me to understand and let other people do as they please, and there have been many similar reports both on the forums and from people I have introduced the theory to in the real world.