> They have too much power? On their land?
It's not their sovereign land, except in the sense that the entirety of the US is 'their land.' Tribes are sovereign over their own land and BAJAA does not change that. It is common for tribes to litigate things outside of their own lands and administered by/for the public, for instance this landmark case https://en.wikipedia.org/wiki/Navajo_Nation_v._United_States...
They used Religious Freedom Restoration Act in that case, and didn't even win.
Some cases that have won use RFRA to legally discriminate against minorities by Evangelical Christians. Native Americans bring lawsuits based on their religion over a sacred site and reclaimed water, just like anyone else can, and yet losing "this landmark case" somehow proves they have too much power?
Their lawyers took the religious objection path perhaps because that might carry greater weight than an environmental protection argument- but at its root this has the look of a watershed issue.
Would you personally be A-OK with tonnes of treated sewerage being dumped upshed from your drinking water extraction point?
Responsible elders / leaders are expected to to do their best to slow roll or stop such changes being made - once it becomes routine its much harder to stop as problems present.