Sigh.... Ignoring the obvious point on people are jerks, you need to understand that calibre is designed as an all inclusive cataloging . management program.
One of the overall design decisions made was that the safest way of ensuring that content being managed by it was only managed by it was by ensuring that all content was stored in one consistent location, namely the calibre library.
While yes, some people have issues with this, many MANY people have accepted that design choice and seen the benefits of it.
See
Want to change the folder structure of the Calibre library? and
Why doesn’t calibre let me store books in my own directory structure?.