Because every device and program uses more or less the same list of trusted root certs. Yes, you can install your own root cert and run your own CA for stuff li

Because every device and program uses more or less the same list of trusted root certs. Yes, you can install your own root cert and run your own CA for stuff like this, but it's a huge pain in the ass to actually install the cert on all your devices. Sure, you can put that cert in your Chrome trust store. But what about Firefox, Safari, IE/Edge? What about your iPhone with Safari and Chrome? What about curl/telnet? What about your daughter's tablet, your son's gaming rig, your wife's e-reader? It's all just so much work. Businesses that have in-house IT departments can get away with it because they provision hundreds/thousands of identical installs of the same software. You don't have that in your house or small office.