Your doors, your windows, you clean them. Our back doors were filthy following building works so I got some cleaning stuff and a cloth and wiped mine down, no-one else did, it took me about 5 minutes. And as Struggler says, the marks etc. are most likely caused by the owner and their visitors anyway.
The concept of “free” is interesting in a strata context. Just because you are not paying for something directly doesn’t mean you are not paying for it. If the owners corporation takes on responsibility for something, you are paying for it through your levies. I would rather the strata pay for important things that really is within its responsibility, and keep costs down in other areas such as this. That also includes things such as sweeping stray leaves. Why would you pay a contractor an inflated price when you can do it yourself with a broom in a few minutes?