Having never worked in a large enough company to have an hr department, this confuses me. My assumption is, a team needs personel and so the team manager makes

Having never worked in a large enough company to have an hr department, this confuses me. My assumption is, a team needs personel and so the team manager makes a request to hr with a list of requirements for said recruit. Or at least that's how it seems like it should be. Along the way, should not someone who put together that list of requirements have some idea of what they were asking for? I've only worked at small enough business we had one general manager in charge of hiring. If one of the sections of our work needed employees, job postings would be created with those specific positions in mind, with the specific requirements of that position figured out by usually the most experienced person in that position and passed along to the manager. Again, this may just be my ignorance, but, if it wasn't the hr person that wrote the requirements, wouldn't it have been someone that should have known better?