Because Singapore outlaw caning women, the schools cannot cane girls without changing other laws but they can cane boys.
The article says this, if it was legal to cane the girls they would also do that but they can't.
But also “we would cane more kids if only it weren’t for those pesky laws” is crazy. The world seems to be on a speedrun to rid itself of all civility. I guess that’s its default state, but where did the civilizing forces go?!
It's often heard from the progressive side of politics, in this general form, as if having everyone equally affected by bad things is a useful policy aspiration:
"<thing>, which is bad, disproportionally affects <girls, poor people, non-white people, etc.>, which is an outrage!"
Apparently, it's easier and more popular to make sure bad things are fairly distributed, rather than reduced or eliminated.