A lot of it is optimizing applications for higher-memory devices. RAM is completely worthless if it's not used, so ideally you should be running your software with close to maximum RAM usage for your device. Of course, the software developer doesn't necessarily know what device you will be using, or how much other software will be running, so they aim for averages.

For example, Java applications will claim much more memory than they need for the heap. Most of that memory will be unused, but it's necessary to have a faster running application. If you've ever run a Java app at consistently 90% heap usage, you know it grinds to an absolute halt with constant collection.

The same is true for caching techniques. Reading from storage is slow, so it often makes sense to put stuff in RAM even if you're not using it very often.