Kaarel Veike on "[Plugin: Wordfence Security] Scan only recognizes about 10% of the malicious files"

I scanned one of my clients site and it showed 9 problematic files. I then manually started to overwrite all the files and removed the ones that were not supposed to be there. So I got around 100 files from the core folders. Why didn't it recognize the other files?

https://wordpress.org/plugins/wordfence/