Ok, I understand. But don't agree with Microsoft in introducing such a
limit... commercial reasons?
This is just an educated guess, since I don't have access to
Microsoft's proprietary code...
The early versions of Word were written for 16-bit Windows, and a lot
of their code -- or at least their basic design -- is still present in
the more recent versions. For purposes of laying out text and
graphics, all locations on the page are calculated from the top left
corner in units of "twips" or twentieths of a point, where a point is
1/72 inch.
I think that for historical reasons, all the variables that hold those
measurements are 16-bit signed integers. The largest value that fits
in such a variable is 32767. When you translate that number of twips
to inches, it's 22.755 inches -- so I think that's where the 22-inch
limitation came from.
Microsoft could change the declarations of all those variables to
32-bit signed integers, which are supported by all versions of Windows
after Win95, and accommodate page sizes of more than 5800 meters!
However, they would also have to comb the code for all the things that
depend on the current definitions, which would be a massive job. I
suspect that they've considered it and failed to find an economic
justification for expending the time and money.