The CV’s static in that it’s not a document needing to be tailored for different positions in the way that a resume is. Rather, according to UNC Writing Center, the CV’s a “fairly detailed overview of your life’s accomplishments, especially those most relevant to the realm of academia,” hence the variance in length; an early-stage grad student’s CV is going to be a lot shorter than a sixth-year student preparing to write a dissertation.
The document only changes as your accomplishments grow—you publish the findings of a scientific study, or a short story, or you receive an award as a Teaching Assistant—whereas a resume can and should be modified often as you job search and apply to different companies and positions. At The Muse, we highly encourage you to tailor your resume for each and every job you apply to, even if the job descriptions are similar. (It’ll not only help you stand out, but also ensure you get through the ATS.)