In many cases you're right. Personally I don't usually care either, within reason*, certainly if it's back-office work.
But it'd be nuts to say presentation isn't important. In our line of work we often acted as representatives of our clients to their clients, shareholders, regulators, government agencies, and the general public, with literally billions of pounds (and sometimes the existence of the client company) at stake. It wasn't uncommon to have to drop everything with no notice and go straight from our office to deal with some crisis for them, and when you rock up to smooth out a situation with panicked clients and difficult stakeholders it's genuinely important to give an impression that's absolutely professional, collected, and in control - and like it or not appearance plays a big role in that.
More generally, your appearance at work signals your attitude to work. You can say it shouldn't as much as you like, but it just does. In a profession where diligence, quality and attention to detail are super important, if you don't appear to care about or take pride in your personal organisation, presentation, health, etc., that isn't going to give your colleagues or clients a good feeling about relying on your work.
- I do have some horror stories, and at one point eventually had to fire someone because of their refusal to address appalling presentation / personal hygiene issues that meant we just couldn't put them in any kind of client environment, even back-office.