Why do we care? So that we can protect our damn systems and powers from opposition in PowerPlay. The block mechanic is an exploit. If I shoot a CMDR in respect of defending my own system, that player will block me, hence escaping justice and continue ruining my system unprovoked. The system will be abused heavily, especially as an advantage for UA bombers. A game that is intended to be "dangerous", should not be called "Elite: Harmless".
That's not how the game works though. The BGS is based on "how many people perform <action>" - where <action> could be anything which affects the BGS. This has never ever been designed around PvP.
The other fact which blasts your post out of the skies is this: Instancing. Limited to, I think, about 32 players per instance, but usually works out less than that. So you could have your player group try to blockade a system, and you'll probably manage to interdict and destroy a couple of enemy players. Meanwhile, the vast majority of your enemies are flitting past you in a parallel universe known as a different instance from yours.
Then there's the different platforms, none of which are going to instance with each other. BOOM.
Then there's the client connectivity modes called "Solo" and "Private Group". BOOM.
And lastly, if every single player and group played in Solo, collectively, they would have the exact same influence over the BGS. Because that's how the game really works.
BOOM.