They could monetize it much better while being less annoying.
Ultimately - Google is getting everything they want from Reddit with this deal without having to buy it outright.
Short of Reddit transforming to an entirely different product (difficult) - I'm not sure where the major growth opportunity is for it.
It'd be somewhat hilarious if google bought reddit just to archive it and shut it down.
They could monetize it much better while being less annoying.
Ultimately - Google is getting everything they want from Reddit with this deal without having to buy it outright.
Short of Reddit transforming to an entirely different product (difficult) - I'm not sure where the major growth opportunity is for it.