Rather than beat grrr over the head for not agreeing with "us," let's just answer the question. The looks of the engines had nothing to do with the decline of passenger service. (The RR's used these same locos in freight service, and that didn't go away.)

I'd think that to be useful in passenger service capable of 100 mph or better speed, new engine technology is available. New diesels get better mileage and better performance than their predecessors, and are cleaner burning too. If visibility was a problem, that can be solved by using video to monitor the "rear" of the engine for the short periods of time that it would be needed.

As a matter of fact, it would be a good idea to put video on the rear of trains anyway as a safety and security measure.

New paint, clean and quiet operation, and green power trains in a retroluck body, why it would be an HHR all over again. GM could have done the job, if they hadn't unloaded EMD!