You don’t always get a change of clothes beforehand (or at all if you won’t be there long). They might just take your belt or anything that could be used to hurt yourself or others, get the photos and then figure out what needs to happen. Depending on the alleged crime, they might get released after a few hours or kept around for questioning.
Letting someone wear their own clothes (as opposed to a prisoner uniform) can be part of the interrogation process too. This and other small comforts may aid with rapport-building while leaving the suspect a trace of hope that they still might be able to talk their way out. Changing into the uniform could drive home the seriousness of the situation that they’d been denying up until that point which might make them less talkative.
Long story short, the word “lawyer” should be a significant part of your vocabulary if you’re in that situation. Phrase your request specifically so there’s no wiggle room about whether you’re bringing up the general idea of the legal profession, asking whether you need one or something along those lines. Ideally also don’t do crime since there’s usually less evidence to defend against when innocent.