Oof - I didn't know that. Kind of a weird requirement, were/are screen readers rendered so ineffective by the content being in a table as opposed to in divs?
Not inneffective as such, it just presented a confusing user experience because the screen reader would assume the table represented data structured in two dimensions and e.g present navigation options for going cellwise left/right and up/down.
This would be pretty confusing if the table was just used to create a margin and most cells only contained spacer gifs. Especially with deeply nested tables (as was the fashion at the time) it could be pretty confusing.
Today you can just add an ARIA-hint indicating a html table is used purely for layout and a screen reader can then treat it just as divs. But this did not exist at the time.
Of course the WCAG just assumed it was not a big deal to avoid tables for layout since CSS2 supported tabular layout through pure CSS. But the reality of a web dominated by IE6 made this a much larger problem.
So it it not really about vague “guilt-pressure”, it is just that many web developers had to follow WCAG as part of their job.