"Because most of the crapware that companies like Dell, HP, and others put on, while irritating, consumes exactly 0% of processor or I/O time, and has zero impact on performance of the device, beyond the hysterical, easily-convinced responses of the placebo effect"
1 - Startup time is affected by all the bloat
2 - Trial for slow/crappy AV, affects IO and CPU usage (more than other anti-virus)
3 - OEM "tools" that make it "easier" to use the computer, consuming a non trivial amount of CPU to check for updates, show several tray icons because of course you need a special utility to switch from builtin screen to external monitor even though the builtin one works better and by the way do you want to sign up to our special partner offers?
I have used countless installs of Windows, through MSDN, retail, Technet, and through vendors like Dell. I happen to avoid being a suggestible simpleton so I don't simply adopt the sophistry that is so common. Sorry if this offends you into hilarious insults.