James had the best explanation; but everyone must realize that as it stands today, only Vista and Win7 are really the only Microsoft OS systems that are actually usable/stable, with Win8 basically abandoned and Win10 with enough serious problems (both actual and Microsoft 'invented') that no corporate plants, even in the Seattle area, will touch it.
Installing w/o a 'signed' driver ought to be a user option. I have several dozen programs running on my V64 machine that I was only able to install by bypassing the 'check'. My security is unaffected since I haven't relied on OS barriers to protect my machines (over 11) in at least 20 years, having had a double-gated multi-router trap system, backed up an extensive machine backup system hosted by multiple NAS machines. Folks can ask why Vista, but at the time MS had just released Win7 and was fixing all the original Vista problems quick time, and Win7 had some major problems worse than Vista.
Yes, way more than most folks could or would have, but like I said, it should be a user option. And yes, btw, I have a V32 machine w/ DVD/Bluray drives that I have Anydvd installed on, so at the end of the day, it won't 'stop' me from doing what I want to, but it is a hassle.