That's a bit different - no one here is suggesting recreating tools, merely using existing tools in a more secure manner and segmenting them off from the general public and sometimes the rest of your network too. Lowering your attack surface is often the cheapest way to stop attacks.
What's being suggested is still a significant increase in spend for infrastructure. Self-hosting is not free. You lose economies of scale on the services. You need to hire an inhouse IT and/or infrastructure/ops team to support them. Your probability of downtime increases significantly, which comes with a cost. It's the same tradeoff you're talking about, with the only difference being the scale of cost.
You need to have one person who can run apt-get upgrade a few times. Most of the good development and operations people are capable of it in my experience at least. It requires at most a few days upfront and a couple hours of monthly work to keep things up to date.
It's not remotely comparable to re-developing the whole system. If your developers can maintain their own machines, they can probably handle this.
