Or any modern sample library (which can get to 80GB for a single piano).
Or any video editing projects and/or templates.
Just some examples of professional stuff (for graphic designers, musicians/producers and videographers) that take huge space.
You don't want to bring around extra drives and cables when you perform.
You don't want vibrations, bad handling etc while performing / touring etc, to crap your HDD.
You get much much faster random reads, which is what playing large sample libraries is all about.
Even Indie games like Cities: Skylines which is PC/Mac only recently sold more than 1M copies in a short amount of time. [2]
I don't really play much but i follow PC Gaming and it has been on the rise for years. Free to play MOBA games like League of Legends have over 8M concurrent players in peak hours with 27M people playing at least game per day. That is more than the viewership of even the most popular TV series, every day of the week.
[1] http://www.dsogaming.com/news/the-witcher-3-out-of-its-4-mil... [2] http://www.polygon.com/2015/4/14/8414099/cities-skylines-hit...
You seem like a very atypical use case. You can't be playing any of the modern AAA games, for example.