>"Hand me that." An order, a directive, as one might issue to a servant.

Do English speakers generally not use "please" and "thank you" with servants?

But in sentences like: “Could you hand me that, please?” The word “please” seems redundant, “could you” already does the job of asking nicely. That is, from my perspective as someone speaking English as a second language.

In that case, it does not materially change the content but it does change the tone to indicate you would appreciate them responding in the affirmative . Adding a “please” to a request also doesn’t make it harder to understand.

You do have a point, though. Passive voice can be a lot more wordy / harder to parse, but people often use it to be more polite sounding.