WordPress suffers from misguided ideology, bad programming, and arrogance, usually all at the same time. Case in point: image handling.
Image handling in WordPress is pure insanity. Left to its own devices, WordPress will create multiple copies of every image at many sizes. This creates a pile of garbage on the server, roughly doubling the disk space used, sometimes worse. And they are so sure they are right about this that there is no way to turn it off - not by settings, not by filters or hooks - no way.