I do wonder if some of those negative raters would've rated Amtrak more fairly, if more of those reviewers were aware Amtrak is at the mercy of freight railroads(for their long distance trains) when it comes to how quickly it'll arrive into stations?
Passengers don't care about that crap. They only care about price, schedule, and reliability. When they are burned, they don't care why. And they are likely not to return.
I agree with VentureForth, but would add "courtesy." I think most people are apt to be more forgiving about, say, a train running late if the reason for it is explained in a polite and timely manner, and less apt to forgive an experience with staff being rude, nasty, or indifferent. Amtrak's inconsistent--and sometimes poor--customer service is both bad for Amtrak in itself, and exacerbates customers' dissatisfaction with other problems.