The same reason why aquariums with 100 fish are more interesting to look at than with 1. Killing them is the least reason, really. If Frontier would add even some smallish social feature, like trading between players and cooperatoive mining, then the more people play the far more useful those features are gonna get.
But for this, FD needs to do something now, because if the culture in this game establishes to be "carebear solo only", then all hope for future progressions in these areas are lost.
"Gonks" can be disabled by massive police and military in core sectors (maybe even anti-interdiction devices in core-core areas around Sol and Achernar). See: There are lots of ways to achieve protection against gonks in an organical in-game manner. What Frontier did was taking the lazy way by adding pretty much a god-mode for traders (seamless solo/multi switching AND banlists?! AND heavy instancing?) It's like buying tons of candy at the supermarket to squelch the children instead of finding a better way to calm them.