Not every Amtrak line even has a quiet car - long-distance lines don't have them, and even some regional lines don't have them (such as the Pacific Surfliner).
I usually go Boston to CT or NY where there is always a quiet car but my point about it not being made obvious enough to those that aren't aware of its existence seems like a fairly simple fix.
There will always be the people that do not feel the rules apply to them but most of the loud people I encounter in the quiet car did not realize where they were.
And some lines only have them at certain hours. For instance, Capitol Corridor (Sacramento <-> Bay Area) only has them for the super-early-morning and late night trains.
