I was thinking of running DP Grasshopper and wondering about when points would be awarded and how many. The consensus in several threads seems to be points for every KO. But the card does not explicitly mention that.

Meanwhile we have SLOSH FF Solomon Grundy which explicitly states that he gives points every time he is KOed if you bring him back.

Why is one explained and the other not?

The wording for Special Powers and Abilities has never been consistent. That is the real answer. Often times figures in the Fast Forces or Starters or Free Comic Book Day Promotion those characters tend to have more explanatory text. This is because they are aimed at newer players who would need that explanation.

As for Grasshopper the reason points are scored is because he is KO'd.

Whenever a Power or Ability triggers when a character is KO'd then points are still scored period.

If a Power or Ability says when the character Would be KO'd or Instead of being KO'd then points are not scored unless the Power or Ability specifically says otherwise.