UNIX predates high-resolution bitmapped displays, high quality stereo wave audio, and hardware 3D rendering.
When UNIX was conceived, computers really were used for computing, in text. Even after the Mac came out in 1984, it took years before WYSIWYG caught on, and many more years before the widespread adoption of displays even remotely suitable for graphical document processing. (Though that won't truthfully come until 300 DPI comes along and we can draw accurately positioned text without colour fringed hacks.)
That said, the belief that one isn't able to use small, dedicated graphical applications doesn't render this goal obsolete. If I want to manipulate some numbers, AutoHotkey (small, lightweight, dedicated tool) lets me bind Win+C to Calculator, a small, lightweight, dedicated tool. I use JujuEdit as a text editor as, while graphical, it loads instantly and is agnostic about text and binary, selecting a display mode suitable for the file, and has (showing its age here!) support for on-disk files up to 2 GB. It has few menus and only a handful of toolbar buttons and that's it – fast, simple, but concealing some very useful features (such as stepping through files by extension, and fully customisable syntax highlighting).
Given the choice, I'll typically opt for whichever program does the least possible above what I absolutely need: Winamp over iTunes for example, and I specifically don't install the media library facility as I have Windows Explorer¹ and Everything for that, the latter being a drive indexer that only indexes filenames, so there's zero noticeable indexing lag, and the hard drive doesn't grind excruciatingly every time you move away from the PC.
Image viewer/tweaker? IrfanView. Even on my creaky 8-year-old PC it's instantaneous at pretty much everything. Ugly as sin and brain-wrenchingly weird, but it's very small and very fast.
¹ Not valid as of Vista as Explorer was castrated