Because time and time again, you need a full functioning web browser to do some things still. There is a lot of stuff you can't do with a phone or tablet browser. Or at the very least, it take 4x as long to do on a mobile device.

I am completely dumbfounded at this revelation, that so many people don't have 'any' computer in their house anymore.

How the f^ you reset your AppleTV when the stupid thing locks up and it tells you have to plug it into a computer running iTunes and reset/refresh it. ???
How you fix your login problem on a site, when the mobile browser won't work to reset password.
How you...   screw it... I'm just shaking my head.