Containerization - taking a deployment that previously was made of lots of apps running on one OS on one physical machine (or a relatively generous fraction of one, as a VM), and turning it into lots of apps each running on their OS on top of the same amount of machine. Containerization significantly increases disk usage for each container and probably increases RAM use a little bit, but to first order does not affect CPU or IOPS or network.

I prefer less disk usage because they enable faster and more frequent backups, and quicker uploads to remote backup. I'm not really running out of free space but I still prefer reducing disk usage.

Second reason is that I can't fit more than two hard disks in my laptop, and more than 4 in my desktop.

Third reason is that internal or external hard disks are not exactly cheap in my country. My country sees ridiculously high import duties and retail markup on all electronics.

Docker. The size of your base image directly affects the size of application images that use it as a base layer.

Embedded systems. Smaller images take less time to be written on SD/eMMC devices.

Less stuff in an image means a smaller surface for bugs and security exploits.

Folks using virtual machines and containers trying to minimize bloat.

less moving parts means less to consider for risks and bugs. and all the other reasons people say small, like faster to load, upload, distribute into container models

Well, expanding disk space can be pretty disruptive even if it is cheap. No need to be wasteful.