I'm not sure how the Crawford rule originated, or why it's
universally used. I suppose that there's a perception that,
in some sense, a player at 1A has outperformed (whether
by luck or skill) a player at 2A and that it would seem somehow
"unnatural" for the rules to (almost) wipe out that advantage
by not restricting doubling.

However, I think that a similar concern of "artificiality" arises
at 2A 2A. Everyone knows that, because immediate doubling
is a version of ultimate play, 2A 2A is equivalent to 1A 1A.
Therefore, obtaining 2A 2A would seem to artificially end the
match prematurely.
I therefore recommend a rule change to make doubling illegal
at 2A 2A. I did recommend this on another thread many years ago.

Paul

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