Remember, problems with the NEC automatically affect the Cardinal, Crescent, Silver Star, Silver Meteor, and Palmetto, and the Chicago-east problems affected the LSL and CL. That's the entire eastern long-distance network. Plus, the Chicago disruption affected all the Michigan services, while the NEC disruption directly affects the Virginia services, Carolinian, Springfield-New Haven, Vermonter, Keystone, and Pennsylvanian. That's before we start discussing connections.
That's really most of the system.
Perhaps you can blame gas prices, but the fact is that a disruption between Philadelphia and New York affects most of Amtrak, and a disruption just east of Chicago affects most of the rest. And if you try to attribute all of the drops to gas prices, then there would have been *no* effect of the disruptions, which would frankly be *weird*.
The declines on the Heartland Flyer, Illinois and Missouri services, San Joaquins (negligible), the Piedmont, and the Cascades might be due to gas prices. But the Piedmont loses a lot when the Carolinian is disrupted.
One of the things going on here is that the drop in gas prices is not that significant, percentagewise, in the states which had higher gas prices to start with. It has its greatest effect in states which had low gas prices to start with. Another is that a drop in gas prices doesn't mean much in a severely traffic-congested area; it's more significant in an area with "open roads".
So I'm willing to believe that cheap gas had an effect on the Heartland Flyer, and maybe the Illinois services, and maybe the Piedmont and the Cascades, but it seems implausible to think they had an effect on New Haven-Springfield
Also, look at which so-called long-distance trains had gains in ridership:
California Zephyr
Southwest Chief
City of New Orleans
Texas Eagle
Palmetto
Four out of the five of these are the ones we'd expect to be unaffected by the disasters. (We'd also expect the Coast Starlight and Sunset Limited to be unaffected, and the Coast Starlight dropped by an insignificant number. I don't have an explanation for the Sunset Limited.)