Well if you are running 15s that would be the score one would have for finishing them in time, so that kinda makes sense. If you are looking at keys above that they would be punching above their weight class and should be expected to cut it close or fail the run. Even dropping down to say the 12 to 14 range they could easily fail since a raider.io score is your best scores not your average scores.
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People want something to blame other than themselves. Making assumptions of why they weren't invited or get bad groups and don't consider the dozens of factors.