A newbie problem: Confused about Graphics Card rigs vs Antminers.

I'm having a difficult time understanding the following predicament:

A 1080 Ti costs about 900 USD where I am. and an Antminer S9 costs about 1800 USD. Considering the price calculator from nicehash I've got that the graphics card brings about 100 USD home and the antminer brings 600 USD. (All numbers are rough approximations.)

If this is the case why do people build graphics card rigs instead of investing in antminers?

Sorry if this is a really dumb question.

Submitted December 01, 2017 at 07:00PM by cryptortoise http://bit.ly/2jCnP0H