Because at work I have to install all kinds of Adobe crap and Java, and other software that uses proprietary files and each piece of crap "requires" something running in the background. They don't actually require it, but Windows allows it anyway. And let's not mention the fact that you really can't do anything about it, because the developers of those software packages are so used to it, that you will probably break them if you try to do things the Right Way(tm).
Here, at work, we image the PCs (we have 3000+) before sending them to the final users. One thing we do in our images is to disable autoupdates (Java, Adobe, Chrome, Firefox &c), and that makes the computers much snappier. We also filter the Windows Updates, pointing WU to an internal server. That makes the machines snappier in general. (Obviously, we keep one eye for security updates and push those to the users on the logon script, as needed).