The problem with this argument (and don’t get angry) is that technically it is cleaner and more hygienic, and yes its easier to clean. They hear that, or they just have to imagine a foreskin and hear the stories about unclean ones and BOOM thats locked in and supported by common sense and anecdotal evidence.
But, the important details are not whether it is cleaner, but whether an intact one is that unhygienic that is warrant being cut. Yes it might be cleaner but a maintained foreskin is not that dirty or unhygienic in the first place and not difficult to. Wash.
So they are technically right on a shallow level which is why this reason is so pervasive.