Also note that one person declining to attend does not open up a corresponding spot on the waitlist. If a school has 100 spots to fill and sends out 120 offers of admission, only after the 21st person declines is there an empty spot. The better the school is at managing its yield, the slimmer the odds of any movement on the WL. That’s why many schools never go to the WL at all and even end up a bit overenrolled (which means they will send out fewer offers the following year). Also note that some WLs are as deep (or deeper) than the size of the incoming class and, as @chemmchimney said above, they are not ranked. WLs benefit the schools, not you.
So, if you are fortunate to have an acceptance, take it, and don’t look back. Love the school that loves you and don’t think twice about removing your name from a list from which you are not coming off.