When I want someone (who needs to pay me) to give me the check, my bank account details are not supplied to them. I just deposit their check. The check has their bank details printed on it, not mine.
When I want someone (who needs to pay me) to transfer money into my account, I need to provide them with my account number.
In the first case, my bank details are kept private, but in the second case, not so much.
In Australia you can make instant bank transfers using phone numbers, email addresses, ABNs etc. Although I’ve never been too bothered about giving out my bank account details - they’re designed to be public.
When I want someone (who needs to pay me) to transfer money into my account, I need to provide them with my account number.
In the first case, my bank details are kept private, but in the second case, not so much.