With aisle seats blocked, the windows are just "going to happen" and you can (probably) sort it yourself when you get onboard (I say "probably" because there's always an off chance of a conductor being stupid, but generally I find that conductors have plenty of common sense). Still, not letting people in the same party grab neighboring seats is a bit odd (versus, say, DL...which blocks middle seats unless you have a party of 3+, when it allows you to book them).

I suspect that Amtrak will give some notice when they're going to back off the restrictions to let people shuffle a bit, but you're right that this could lead to some real disasters on a packed train when this backs off.

Honestly, it would probably make more sense to just drop the seat assignments once this blows over. It sorta works in Acela First because you don't have that much shorter-haul turnover but otherwise it's just a mess.

My guess is that it's the low load factors that are at issue. If roughly half of the seats are guaranteed to be empty and another third seem to be empty on top of that, then I think folks are gonna feel very little compunction about moving around (especially if they're presuming that the other passengers will have been given a random seat assignment as well and not really care if they get it). Bear in mind that unlike in Acela First (where you have 2-1 seating, so there are a bunch of seating "products" in the single car), in Business you have basically "a bunch of seats" and "here's a table". I think another issue is that this mostly got "dumped" on people en masse (versus Acela First, where it got rolled out slowly)...and if folks have older bookings, I don't think they feel bound by an assignment that was dumped on them post-booking, which is just aggravating the other issues.

Also, to quote an old friend, a service which is not desired is not a service.

The net result is that if you have a passenger who's used to "just sort your seat when you get on board" and who then has a random seat assignment stuffed in their hand on a train that you're told is running at perhaps 1/3 of capacity ("20%" is pretty common for next week, and thats vs the reduced capacity), the social incentives for compliance are going to be close to nil (if anything, someone being in "my" seat outside of a single seat in a 2-1 configuration is simply an excuse to sit where I want). When you add in the inability to select the quiet car (where there is a material difference) and have Amtrak telling you to go back and mess with it after you've booked...well, if I had to guess, what's happening is conductors are saying "Yeah, the QC is 2/3 empty and I can fit everyone who booked BC/Coach on this train in that car...just take your seat check and find an open seat" and banking that if you have a reservation "clash" you'll sort it out for yourselves without too much trouble.