One thing that AWS, Google and Azure do that your own systems don't is release their updates whenever it suits them, often taking down your business down in the middle of the day with their own problems. You can't fix it, you can't rollback what you just did and get back up and running you just have to sit and wait.

That is quite different to a business that turns off its boxes for an hour at 0100 Sunday morning to do updates and release new software. The downtime isn't equivalent because it really matters when it is and if that hurts your use case or not. Your own system might be down for more hours a year than AWS, but its not down Monday to Friday on an evening when you do most your sales because you refuse to touch anything during that period and do all the work outside that and schedule your updates.