The idea behind the security of this website is that rather than protecting the images themselves (nearly impossible) we just protect their association with gender / you / the internet. If you upload to imgur it'll only be accessible from here.
If everyone uploads to imgur, say, then they're all just another image on imgur. There's no relation to this website, and once this website deletes the link there will be no way to get there. If a malicious person made it through the Trust filter and stole the image - it wouldn't mean anything. It would just be an imgur image.
Unfortunately, it's impossible to avoid people stealing images. Snapchat ran into this same problem. Even if we could track when a screenshot is taken, people can take pictures of the screen. So why try? We have an arguably better way of keeping it safe.
(also, hosting images is expensive)