SNIP
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>Just in passing, I did notice on reading the above page, that the current date of Thanksgiving is in deference to American business, too close to Christmas & they wouldn't be able to maximise profits from the two celebrations.

Yep, it says it was moved in 1939 (only) for that specific purpose. As noticeable in that description, it was on Nov 22 in the year of the proclamation shown in the article.
When the US economy was being "stressed" several years back (10 or so) and Thanksgiving was falling very late that year too (as this one), economists there were actually adjusting consumption numbers to allow for the shorter time between the two holidays (because economically it is treated as one long bonanza). Appearances were so important and "better news" could only help to spur people to spend.