It seems to just be an anti rmt and antispammimg feature like fishing had in 11 to keep people from staying out there and tripling the item production. I don't agree that it should hurt your sp because that is what surplus is for. however, I do think that putting breaks on gathering is necessary to keep the Econ under control.

It seems to be based on number of attempts. I go into field fatigue really quickly on low grade mining points even though I get no sp and I have less total strikes.