[sesqu]

An update procedures takes up noticeable amounts of CPU time and bandwidth. Automatic updates means your system slows down arbitrarily, often with no indication as to why. Users are able to make observations at the level of "since I installed software X, my computer doesn't work properly anymore" and interpret that as a virus infection.

Maybe they can't weigh the downsides of new and old versions, but they can weigh the downsides of now and later. Usually they go for later, which is a different problem.