...biggest reason being Windows Update, that sorry piece of ****!
I know many people here mention cleaning out any bloatware... but to be perfectly honest, I can't even tell what bloatware I have on my system, if I had any at all.
On a smartphone, bloat is much more obvious and is almost always a nuisance at one time or another, this is why many people try to 'root' their phones.. but on a computer, I honestly would not a worry a thing about bloatware. Just my humble opinion.