I also don't understand the outdated 500kb image limit.
I understand that some forummers use a slow connection, so the 500kb limit may apply to *viewing* images, but for uploading, most sites have an almost unlimited upload size and the forum software downscales the image if it is too large. But CN still lags behind.
As a workaround I upload an image to my own rented hosting VPS or sometimes even https://imgbb.com/ where you can upload images without account.
There are still members with slow internet connections for whom large images represent problems.
A 1224 x 918 photo of 312 KB, it shows plenty of detail.