The problem is, leaving them around make people think it's ok to upload file with name like Hello.jpg, en mass.
I once spent hours carefully rename files and replace all the links to those files, only for someone else to upload VclsnapRandomNumbers.jpg twice as many within minutes. So it's clear that "just renaming them" is neither enough nor ineffective.
Now, if you want me to restore deleted images, then please give me specific filename and what it is about (for example, the one on Gundam Titans Type should at least mentioned the manga's title), so I can restore and rename them properly. If you found an image with bad filename, them rename it first. I won't delete anything with descriptive filename, even if it is vague.