I just find the current (lack of) system creates a stressful and unpleasant experience. First you have to turn up way ahead of time to secure a spot in line (and surely one advantage of train travel is that unlike taking the plane you shouldn't have to turn up very early). Then there is the stress of finding a seat on board, especially if you're in a group. When I took the Maple Leaf I had to struggle with my luggage, and then was herded by the staff into a specific very busy car, where I was lucky to get the last window seat. Other cars were half empty yet lots of people were very upset as they ended up with no window and were told they had to sit in a specific car.
Sure, if I was a reader of this forum I would know I could get a red cap to take my luggage and secure my seat, but how would I know this as a member of Joe public taking the train for the first time?
In a few months I'm traveling with my parents from Toronto to Montreal and Montreal to NYC. Toronto to Montreal is reserved seating. We know we have a bay of 4, and we can turn up just before the train. I'm already dreading Montreal to NYC. Will we get 4 seats together? How early do we have to turn up? Will my parents, in their 70's, be ok with standing in line for 45 minutes or more? The main reason for taking the train over the plane is to see the scenery and relax but Amtrak makes it anything but relaxing.
Introducing seat reservations is quite possible, so many other railways manage it, often reserving the same seat several times during one journey and often even allowing you to pick your seat online.