I think in the UK sense 'tabled' is borne out of a pretty literal meaning - based on the proposal literally being brought to the table where the committee are meeting to assess (and potentially vote) on its viability.

Yeah, perhaps. But the table also has all kinds of other things on and around it. Random papers of varying importance, microphones, Representative Smith's porn phone with the privacy filter, and maybe a ham sandwich.

A table (if there even is one present at all) seems like about the least important part of a group discussion of an idea.