It may surprise people, but it takes a LOT of disk storage space to store photos (2 - 5 megabytes (MB) each) or videos. Take a normal, 1-1/2 hour movie: as an old VCR tape it wold be about 900 MB. Same movie as an HD would be about 3 Gigabytes (GB) and bump that up to 4K resolution and it jumps to a little less than 6GB PER MOVIE! Those car videos that MUSBJIM and I do? About 1.5 GB each. (I know this because for 15 years, disk storage was my life).
Multiply that by lots of users posting photos and video and you can see that the storage requirements are enormous and expensive. Even with the cost of storage plummeting over the years as more data is crammed onto the same physical platters, it's still expensive. Youtube, as just one example, is adding the equivalent in storage of an average University library every day (1 terabyte or 1000 gigabytes). 20 years ago, that would have been around $1 million bucks, but today it's more like $500 bucks. That's how much storage costs have plummeted.
If you can leave the media where-ever it is stored and just serve it up from there on another site with just a link, it helps sites like this a LOT in saved resources. That's how we link Youtube videos on here so the SOC server doesn't have to have tons more storage. Still, at the current rate of storage usage by social media and everything else, it's a wonderful time to be in the storage business.