Because printers are an utter scam, that's why. I've gone through a few. One was an HP that was broken right out of the box. Another was a Lexmark that I returned immediately because their mandatory 600MB software fucked the system so badly I had to recover from a backup. Another was a second HP that worked decently until the paper jammed, at which point we discovered there is absolutely no way short of buying a rivet tool and ripping it apart to unjam it. I now have a Canon that works fantastic, except for having no support at all under Linux.

The nonsense they can get away with when it comes to ink is just outrageous. Consumerist recently ran an article about how it's often cheaper to replace the entire printer than the ink cartridge. Printer manufacturers, of course, responded to that by not filling the cartridges in new printers. Colour printers mix all the colours to make black to run through ink faster. Chips in the cartridges deliberately creating artificial compatibility issues, reporting "out of ink" when there's still plenty left, etc.
Cartridges have been known to "clog up" if not used once every month or so, and so some manufacturers have "fixed" that problem by having the printer automatically squirt a little once per day. It only needs to be done monthly but hell let's do it daily, not like it's wasting anything expensive!
Printers that refuse to print when the ink level is "low" even though it's plenty enough, or refuse to print in black because they're out of red. Printer/scanner combos that refuse to scan without a full ink cartridge. I really cannot comprehend how they can be allowed to do these things. I've heard (not confirmed, but it's not hard to believe) the ink for some of these things, per litre, costs more than human blood. Really. WTF.

Oh, and modern printers leave "invisible" watermarks on your printouts so they can be traced back to you. Look it up.

Fuck printers. </rant>

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IIRC it hooked itself into many places in unsafe/faulty ways, started a few background processes that used 100% CPU, and broke quite a few things. Unlike most devices the driver files weren't conveniently located on the CD so you could just point Windows at it and bypass the installer. You had to install all the bloatware. (No options - all or nothing, no way to uninstall individual components after installation.)

I have actually seen some decent business-model printers, but those are terribly expensive.

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My first 32-bit computer was an HP and the software wasn't that bad, besides the OS being WinME. McAfee sucked but the rest seemed alright. The hardware, on the other hand... that was the one that came with the broken-from-day-one printer and needed an additional fan installed (which required cutting a hole in the case).
It did have a thermal reboot (not even shutdown), but that didn't kick in until the IDE cables were beginning to melt.
I swear it had some other hardware issue as well, that would cause occasional graphic distortion and bugs. When I one day opened it up to clean, a piece of the CPU just fell off. Naturally it no longer booted. We gave up, threw it out, and replaced it with the machine I still have now, built from parts.
(Probably the only parts of this machine that haven't been replaced since then are the mainboard, CPU/heatsink/fan, and case. The floppy drive is still installed, but I don't think the floppy controller ever worked, nor do I care. The original 20GB hard drive, which was actually taken out of that HP machine, still works and is in my PS2.)

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Yeah, they really cheap out on the parts. I always forget to mention the power supply of that machine: 100 watts. The whole damn thing had as much power as a light bulb. I suspect that was the cause of a lot of the issues.

I've never had a good experience with HP, but I haven't used one of their products in years, before they merged with Compaq. A friend of mine has an HP netbook which is prone to BSODing, but the message indicates it's the fault of a video driver.

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