After doing new MR, last commit from last MR still added to new MR

hello guys, so im quite newbie to git workflow, specifically merge request, as i quite know and learn, merge request is for add/join all changes/files in some (source) branches to another (target) branch, and after doing MR, the target branch is should contains all changes/files from source branches. so my logic is when im doing some MR lets say sprint-feature branch to development branch, it will happens:

  1. add all changes/files from sprint-feature branch to development branch, which mean development branch should have or same source code with sprint-feature branch ( if im not delete source branch )
  2. after MR, all commit in source branch will add to target branch, so we cant MR using same commit right ?

so why im asking this because, after i doing a MR from sprint-feature branch to development branch, and if i create another new MR again, it contains all commit from last MR.

so anyone can explain to me, with simple terms how MR works and why i have experience that. thanks