I'm still very new to IPFS and still learning about how it functions so I'm not 100% what would be the caus e of this.

• could it be that your instance has downloaded and cache recent videos but somehow they have not been requested often from your node? This could be because the videos are not popular or maybe most people who watch those videos are not close enough to your node?

Anyway, I've done a little bit of research to try answer that question and found this:
https://github.com/ipfs/faq/issues/104#issuecomment-204267853

I've also noticed the same thing on my three instances. The other observation I have is on my AWS EC2 free tier instance, I only have 1GB of RAM and IPFS is using all of it, I started using SWAP but it does only help a bit. They still need some improvement.