What is the difference wrt proposal “have Decimal and Fraction as builtins”?
Not only fractions module in the stdlib has only one public class or function. E.g. sched or html.parser.
It’s again a question “why not have the Fraction as a builtin?” But to support this you need some other arguments (see e.g. Revise true division for ints? Lets return (optionally) a Fraction!), just the number of public interfaces in the fractions module is irrelevant here.