Yeah, of course it varies place to place but I think for the majority of at least somewhat developed countries and urban areas in less developed countries 50Mbps is a reasonable figure for "normal home internet" - even at 25Mbps you're looking at 4½ hours for 50GB which is very doable if you leave it going while you're at work or just in the background over the course of an evening
Edit: I was curious and looked it up. Global average download is around 50-60Mbps and upload is 10-12Mbps.
Images are a lot easier to create "good enough" generations of locally compared to text and video... I imagine the driving force is probably horny people like 99% of other innovations on the internet