it's a historical quirk that we have percentages - they have been around for a while
Wikipedia claims that they were evident in Ancient Rome,
emperor Augustus levied a tax of 1/100 on goods sold at auction
as denominations of money grew in the Middle Ages, computations with a denominator of 100 became more standard and from the late 15th century it became common for arithmetic texts to include such computations
many of these texts applied these methods to profit and loss and by the 17th century it was standard to quote interest rates in hundredths
as '% of' operators, my view is that percentages should be turned into decimals from the outset, and ongoingly...
note: there is no number 9 involved and no repeated digits are allowed