Sure, they are less likely to fail in the stable environment, but you can't get to it until you pull up the entire vessel. On land 5.9% of servers required a technician to walk over there and replace components. At sea 0.7% of servers failed irrecoverably.

On the other hand 0.7% dead hardware sounds like a marginal cost. What likely killed it was the cost to deploy and recover them, plus all the hassle with sea cables for data and power. Building glorified warehouses with redundant power and AC is likely a lot cheaper than deploying these metal tanks in the ocean.

Less noise and dust down there - I think the air is purged with nitrogen as well so no oxidization. They could do the same thing cheaper on land and recycle the waste heat. Edit: just read the article - they also state temperature stability as a factor.

Having the servers more easy to access and repair also makes them more likely to fail. Also spaces that humans can enter require a bunch of regulation that takes up space and adds to the expense. So the math could easily work out in favor of a sealed box of computers that no-one is allowed to access and any broken servers just get switched off.

That it's significantly cheaper to deal with the failures than it is to prevent them.

And I wonder if they meant 187.5% (this is better) or 87.5% (this is worse).

I would expect price and practicability of physical intervention