People leave for all sorts of reasons: Moving for family reasons, becoming stay-at-home parents, moving for a spouse's job, retiring, starting their own companies, or even just getting bored and wanting to do something different. Or it could be as simple as getting promoted to a different role.
It's unrealistic to make engineering decisions with the assumption that the same engineers will be around and stuck on the same project forever.
Like the OP said: Every hour they have to spend working on the colocation setup is an hour they aren't spending on your company's competitive advantage, so you have to hire more engineers (and more managers) to compensate.
> If a company can't hire datacenter techs...
How many techs do you think you need for reasonable on-call coverage? 3? 6? Add a manager in the mix because you need someone to manage them.
The costs add up quickly.
It's weird to see people championing colocation as a cost saver and then pivoting to arguments that you just need to hire more engineers and techs and manage them.
Employees are expensive. One of the primary benefits of cloud is that you don't have to hire and manage all of these employees to do all of these things at the colo.