When you trade it in, the buyer is purchasing raw compute power, and the buying agent expects to have to expend their company's money to make it 'user ready'.
Used computers that sell for top dollar are already 'user-ready.' The buyer can imagine taking it out of the box and getting their work done immediately, or perhaps after only some setup and possibly a software upgrade.
Computers that appear to have festering problems or are somehow less than User-ready sell only for "wholesale" prices to buyers willing to put in the time and effort (and knowledge) to fix them up for actual use.
So if yours is made to appear "user-ready", and you point that out, you will get more interest and likely a higher price.
Sale-able computers must have a copy of MacOS installed, But NOT set up. DO NOT leave the currently-running macOS on it, because that version is tagged with YOUR Apple-ID, and will be of no use to the buyer since it can not be updated without YOUR Apple-ID.
What to do before you sell, give away, trade in, or recycle your Mac - Apple Support