> Is it considered that hard and expensive to just run a full backend stack on your own machines

Well time is money. Things that are not core to your business like managing email servers are better off outsourced; not because they are hard, but because it frees your time from setting up, managing, securing and monitoring your email servers, and allows you to put it in something that actually matters to what you do.

In a startup world, it's probably expensive in terms of time. At this point, you may or may not have revenue yet. So you want to spend more time dedicated to validating your idea so you can pay the bills or find the next Facebook/Twitter/Google/etc.

I do agree that eventually everything should be self-managed to ensure service is never disrupted. It's critical to ensure that the service is always online for the customer and maintaining that control, in my opinion, is important.

It's a set of trade-offs. I could run my own cloud stack and all too but I don't want to deal with it.

I could push to a self-owned git repo, but bitbucket and github have lots of nice tools already built around them. When they have issues with their servers/disks, most of the time I won't know and don't have to do anything.

Now, by all means, have contingency plans. Keep pushing to that self-owned git repo, have back ups and such, but I think people just don't want to worry about things.

I'm with you. It's best to run your own copies of the software on your own hardware (or VPS). People are depending more and more on services as a software substitute.

Furthermore, a lot of these free (gratis) applications can be replaced by free (libre) applications. That way you actually can run the software on your own machines.

I agree. All those external services have to be up for the users get a bad experience.