Look at a station map or visit the station. When you have 2 or more trains boarding near simultaneously the queue to get down the the platform level is pretty long and snakes. There's a difference between waiting for a train at a terminating station where you don't know the the track assignment vs boarding a train at a non terminating stop or minor station where the is no grand hall. Moynihan has underground non open air platforms so you need to keep people waiting above in the hall since there's not a lot of room at platform level.

This is the map:

See that area on the right called ticketed waiting room? That is where everyone with a train ticket can sit at a bench/chair or grab a table/desk to do some work. On the other side there is a food hall. As someone that travels out of that station regularly, I think the design totally makes sense based on the size, amount of foot traffic, and etc. If I need a place to sit before my train boards, I know where to sit.

The waiting area with seats:

These are the one way escalators that you don't line with benches where people queue to get up. You don't want people sitting and possibly blocking the escalators either.

The real crime here to complain about is that the Old Penn Station was destroyed to put in a MSG. We have a stadium at the expense of a well designed train station. Moynihan being built next door on a small footprint really was a breath of fresh air to a terrible train station. You don't get situations like this in Moynihan: https://www.westsidespirit.com/binrepository/576x432/0c0/0d0/none/3502612/ODJP/penn1_4-3802539_20211210112648.jpg

Instead you get this queue for 1 train boarding on track 13/14. (it is worse if there's multiple trains boarding simultaneously): If there are multiple simultaneous boardings, I am not sure if they use space between escalators to snake the line instead of wrapping around all escalators (at times I do see some of those lane rope things in use to encourage people to no clog up the middle to foot traffic) That does not compare to a minor philadelphia suburb platform where you wait on the platform because the already full train isn't going to stop for more than 2 minutes to pick up a few passengers. That would be a massive safety risk to allow this kind of seating on platform in NYC rail system with underground platforms. And this is not even considering how to move people off a train before moving the next group on the train. Also crew changes since NYC is a terminating station for a lot of lines.

You can have folks queuing up and still have a lot of room for people to navigate through the main hall. Probably as a much a security and anti-terrorism feature as well as a design to not obstruct boarding or create bottle necks for emergency egress.

I don't think you'll find many new yorkers complaining about a lack of seating in Moynihan right on the main hall where all the foot traffic is. We like it when people get the fuck out of our way while we try to get from point A to B.

Edit: also I don't think people understand the scale of NYC's population and train rider ship. Moynihan ridership is 8 million annually. 2nd place is DC with 3.6 million. Moynihan is a amtrak only station so it's built for luggage, but even then Moynihan is probably a smaller station than either DC or Philly, yet has over double the ridership. I don't think folks appreciate how much traffic goes through a relatively small train station, but I think that factors into the design of NYC stations vs any other picture you have of spacious stations that have less than half the ridership in buildings of comparable size.

Edit 2: In this thread people that don't understand the difference between Amtrak, regional commuter trains, or subways, or the difference between urban vs suburban stations, above ground vs underground stations, and the fact that NYC has over double the annual amtrak ridership than the 2nd and 3rd most used amtrak stations. Not to mention, NYC has tons of benches and public seating. Sections of broadway are closed down with chairs and tables out, bryant park isn't too far away with tons of public seating. Not surprised that the small train station is designed to have seating options only for riders of the train.