You should move the question to Products. "Community" is for issues with the Marketo Nation (this website) itself -- and yes, this is confusing!
It's true that Marketo doesn't have a native way to do this, but that's not really related to email attachments at all.
There is a way to upload images to a Marketo form that I developed a while back, but now if you search for "uploadcare" you'll see a newer approach to this topic (also submitted by me!).