Any reason why printf() does not support formats with thousands separator?

$SUBJ says it all - I've recently discovered that a format such
as %'.2f" results in this:

php -r "printf(\"%'.2f\", 23232323.237);"
23232323.237000

I know that number_format() will do the same, but I am given the format
spec as an interface, I would need to try to parse it and then decide
whether to use printf() or number_format(). 


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Per Jessen, Zürich (19.9°C)
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