Most code needs ongoing maintenance - if folks aren't writing tests to begin with, then they probably aren't going to update them as functionality changes over time if Fred isn't around. And automation might be great for the current situation, but eventually need some improvements that nobody is willing to do. Eventually the tool seems less useful and people stop using it.

Requirement changes, I change the code, test fails, I remove the test, Fred isn't there to speak for the test.

Automation fails, I turn it off and run the thing by hand. Fred isn't there to turn the automation back on, or yell at me for running it by hand instead of fixing the automation.

I'm not the OP, but I think they mean that the tests will slowly become out of date (if nobody else is updating them.)