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

Question

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().