I would argue that this is less an example of why linking out may be bad for engagement and more an example of google abusing its intermediary/market position to keep users on their own pages longer
In terms of a single search, I don't think Google really benefits from preventing a click-through - the journey is over once the user has their information. If anything, making them click through to an ad-infested page would probably get a few fractions of a cent extra given how deeply Google is embedded in the ads ecosystem.
But giving the user the result faster means they're more likely to come back when they need the next piece of information, and give them more time to search for the next information. That benefits Google, but only because it benefits the user.