@Freestyle
a lock for your shoes...? Why?
So that people don't fuck with it. Because of the Japanese obsession with clean shoes and shoe lockers in schools, either your required-or-get-chastised-and-have-to-pay-for-a-replacement-pair of clean "indoor shoes" are in there or your potentially expensive outdoor shoes are in there.
And, depending on the person, fucking with someone's shoes - especially if they are some Nike bullshit that can cost hundreds of dollars - is a good way for bullies to target someone and a good way for someone to end up in the emergency room. I saw people back in school (admittedly over 15 years ago now, holy shit) get petty enough to do shit over far less.
My guess is that the reason it isn't shown if that the shoe lockers either aren't configured to allow it or it's, most likely, bizarre and dumb school regulations. This is the same country where there's been incidents of schools not allowing their students to dye their hair whatsoever and "politely asking" foreign/mixed students with non-black hair to break school regulations and dye their hair to match everyone else's just to have uniformity (which to my western brain is hilariously ridiculous and infuriatingly hypocritical in the same breath). And, hell, many schools even require you to prove via doctors note that your hair is genetically non-black and you aren't dying it. So I can see them taking issue over students having locks on lockers for... whatever petty reason.