Issue here is that some server has to host these images. Imgur and external sources are ideal because PMC doesn't have to keep that content and manage it. Afterall, images cost bandwidth and if we were presenting all the images from our servers, our servers would be doing more work and costing us more.
PMC offers image hosting for submission images because we want to provide content quickly to the users. It will always be faster if you can dish up the content from your own server. However, hosting any and all images opens a lot more complexity when it comes to image ownership, removals, managing the storage space, etc. Bottom line, it would be expensive and the trade off is more obtrusive ads to pay for it.
Before it even gets suggested, PMC will not accept any money or donations from its users. Too many complications and headaches. Better to just not do it at all.
Generally there is no requirement to use external images in a description. It certainly helps, but it is optional. Whereas submission images are required. This means we have to focus on providing storage and bandwidth to the essential pieces, but leave the optional stuff up to the users to provide.
A way to import images from your photo gallery, or files easier