I wonder how much of this is simply due to increasing expectations on interface and portability. Icons, borders, and fonts were tiny in the 90s and looked tiny. Programs ran for particular platforms and were often coded in the native platform's APIs and linked to specific binaries of a specific OS version. Now with expectations of high res iconogrophay, detailed and smooth fonts, as well as the expectation that an OS update shouldn't effect any of my apps - we inherently have bigger programs. The alternative approach could be taken, but it wouldn't be viewed as a mark of quality.

Games like Destiny weighs in at >100GB with it's latest updates due to map and image needs, and the slack client runs smoothly across 5 Operating systems.