I have a number of books (one of them is really a binder) detailing Amtraks pre-heritage fleet fluctuations. It’s a fascinating subject on its own; I was going to write a book but I stumbled onto a rabbit hole doing it, ended up promising somebody I wouldn’t discuss what was in it, and decided the book would have been to false to write without including what I found.
There were some really weird pieces of equipment (Amfleet I coach-snack-sleeper, anyone?) in early Amtrak days, and quite a bit of stuff on roster that didn’t turn a wheel in revenue service or even not in revenue service. The Amtrak gallery fleet included snack sections, parlor sections, and even a dining section (tiny kitchen, table service) but as far as I know never included full cars of any of these things- one side would always be coach seating. These pieces of equipment made more sense than Amfleets or standard streamliners on the frequent-stop low-platform routes they served due to their ability to accommodate shorter dwell times.
I suspect that meeting the above was as much a factor in CNWs ordering of this equipment as an intention to convert them to commuter equipment. Also keep in mind that back in the early 70s commuter trains sometimes ran with bar cars, parlour cars, or both. Metra ran snack Cars for quite a while, LIRR ran them and actual parlour cars more or less until the debut of the current double decker cars, and Metro North ran Bar Cars up until almost the withdrawal of M2s; I believe the last run was in 2014.