Four trains per day on the route I am referencing
I don't know why people are bringing up hypotheticals that are so far from reality like one train per week. That's just not how trains are scheduled with Amtrak. I take the train on a regular basis and your example is entirely removed from the reality that I have personally observed.
How many planes are there per day on a single route in the Midwest? Because I doubt its hundreds
Certainly compared to other modes in most circumstances. If, on a particular route, there's one train a week and 100 planes a day, the train can still be packed while "train passengers" are still rare.
IIRC, Amtrak was created because the railroads were losing money on passenger traffic and wanted to get rid of the service. I imagine that's because the service had a lot more competitors than it did in rail's heyday.