The reason they are being ignored is that the mitigation measures imply considerable expense. Even though it was a federal project, North Dakota would have had to pay a third, which just for North Dakota would have amounted to $70 million or $80 million, and probably more.
Même s'il s'agissait d'un projet fédéral, le Dakota du Nord aurait été tenu d'assumer le tiers des frais, soit 70 ou 80 millions de dollars, voire davantage.