"Please open the door slowly."
I had that sense too. I'm doing the placement test for Japanese (as a speaker of 12 years) just to see how it is (to give me an idea with my other languages what is and isn't there) and some of the phrases are unnatural to my brain, this being one of them. I couldn't believe を wasn't an option. I remember so much emphasis being put on transitive and intransitive verbs using doors and windows and the verb open that this is ingrained into my brain. Doa ga aku - the door opens. I open the door - door o akeru. Please open the door thus transitive - door o akete kudasai.
In learning -て form, Duo has had us use ください with the expected translation of 'please'. Previously, Duo expected ください to be translated as 'Can I get...?'.
Now i understand it can mean both, but is there a specific reason that it's being used in these examples instead of, say, おねがい?
I've heard one suggestion that ください is paired with て similar to 好き and が - although Duo has broken that "rule" before, so I'm not sure.