@Toutatis, it's similar to how two people (with different ratings) will not get the same rewards/penalties for winning/losing/drawing against the same opponent. (I'd feel like a cross-posting spammer if I copy-pasted so I just shared a link to how I think puzzle ratings get calculated.)
Chess can be lax or strict. You can sometimes salvage a win/draw from a seemingly lost game. A difference of one square (f7 or g7) can be crucial: the "sphere of influence" of pieces and pawns can be quite tricky. A move too soon or too late can have devastating cumulative and/or immediate repercussions. There might be convoluted paths that lead to the same/similar situations. Chess is beautiful that way. :3