The problem is margin
I'm an end user computing person, and it's amazing how thin margins on consumer hardware actually are. That doesn't justify this, but you can see how a vendor could see a quick win, any win, in the crap hardware territory that they push out to consumers. This is the stuff you buy at Best Buy/Staples - the $200 desktop or $300 disposable laptop. The $500 business desktop or $900 ThinkPad T series is a whole other class of machine.
Lenovo, HP and the like make good business hardware, and for the most part, the default image isn't loaded with this garbage. The worst I've seen is a free McAfee or Norton trial, and I think the main reason they do this is for the small/medium business types who just use the factory image as-is. They know that most business customers are going to blow away the factory image anyway once they steal the useful stuff off of it and use it to integrate the hardware into their standard image.
If PC manufacturers could somehow just dump the crap-grade consumer hardware, they'd be in good shape. Unfortunately, enough people still refuse to pay more than $400 for a machine. I do give Microsoft points though -- they're helping by allowing savvy users to legally turn in their OEM license key to get a non-bloatware version of Windows. Unfortunately, they're not able to help integrating all the vendor drivers and utilities.
Side note - even on business laptops, it's amazing how much of the hardware requires actual software programs to control it these days. I just worked on getting a new HP EliteBook into our "supported hardware" category, and I needed about 5 non-crapware applications installed just to let me control the hardware!