One frame for a 4K monitor takes 33MB of memory. You need three of them for triple buffering used back in 2002, so half of your 256MB went to simply displaying a bloody UI. But there's more! Today we're using viewport composition, so the more apps you run, the more memory you need just to display the UI. Now this is what OS will use to render the final result, but your app will use additional memory for high res icons, fonts, photos, videos, etc. 4GB today is nothing.
I can tell you an anecdote. My partner was making a set of photo collages, about 7 art works to be printed in large format (think 5m+ per side). So 7 photo collages with source material saved on an external drive took 500 gigs. Tell me more about 256MB, lol.