Typical reasons for 9th grade reclassing?

I’ve heard that some schools have a high number of reclassed students, which is something to consider for social fit. I read a post on CC somewhere that Hotchkiss can be up to 40%!

Any thoughts or insights into what are the most common reasons a student might choose to apply while in 9th grade as an incoming 9th grader, rather than apply to 10th grade?

Are they often students who didn’t get accepted into BS schools they liked/could accept in 8th grade? Students who wanted to be stronger academically or athletically before applying because they didn’t think they’d get in or want to get in from 8th grade? Students from schools that end at 9th grade and wanted a full 4-year experience at boarding school? Only became aware of BS after 8th grade? Students who didn’t feel ready to apply in 8th grade for personal or developmental reasons?

I imagine there are many reasons… but maybe some more than others?? I get waiting until a bit older to apply to BS, but why the desire to reclass?