in the late 1980s or early 1990s PG&E had an abundance of juice it wanted to sell on long term contracts. They paid for an electrification study and discovered that essentially given the mountain grades, the max trains size was something like 50 cars. (I don't remember the specific number, but is was much smaller than what was running at the time.) Even if you added an additional engine, it didn't help because they were all sucking juice from the same source. Four units ended up producing the same HP as three and so on. What the railroads would save on fuel, they burn up in crew costs and it would have added to the congestion as well.

Believe me, every Class One has done multiple electrification studies. and if any of them ever made sense financially they'd be lobbying congress for the necessary tax breaks. Maybe if crews costs stop being an issue they'll look at it again.