[randomImmigrant]

Simple. Energetics. Gaseous exchange has many energetic benefits that you give up if you have a mostly inert atmosphere.

If all your reactive chemistry comes from water/minerals, you’re also a heck of a lot more tethered, as both these cycle slower than the atmosphere.

A dynamic atmosphere is a huge component of the energetic efficiency of life on earth. And while it’s totally plausible other chemistries can match this, what’s implausible is for no chemistry to match it.

And when it comes to complex life on earth, it literally didn’t happen till oxygen percentages got sufficiently high in the atmosphere, a two billion year long process set off by Cyanobacteria. You can’t get big bodies if you can’t get this kind of energy.