We wanted multi-tasking OSes, so that we could start one program without having to exit the previous one first. That made the OS a lot bigger.
Eventually, we got web browsers. Then Netscape added caching, and browsers got faster and less frustrating, but also bigger. And then they added multiple tabs, and that was more convenient, but it took more memory.
And they kept adding media types... and unicode support... and...
We used to write code in text editors. Well, a good IDE takes a lot more space, but it's easier to use.
In short: We kept finding things that the computer could do for us, so that we wouldn't have to do them ourselves, or do it more conveniently, or do something at all that we couldn't do before. The price of that was that we're dragging around the code to do all those things. By now, it's a rather large amount to drag around...