What the f…? What kind of image files? Uncompressed RAW data? 100 Megapixel?
A forum is not a digital archive for storing HUGE pictures (or other files). More than just storing the files is the repeated delivery. If a thread contains multiple images with several MB and gets opened a few hundred times, this does show in traffic. That can get expensive. Not even talking about videos here.
Different calculation than just: "What does a single 16TB HDD cost? No problem allowing big files!"
I am probably the only one thinking that hard about such, but I usually try to cut, resize and compress images way beyond 1MB and very short videos below 10MB if there is not a good reason for more. This helps for people with slow connection as well.
For big files external hosting makes sense.