I don't believe hard drives are failing more often because they have much greater densities (capacities). I think hard drives are failing more often because makers have cut too many corners in quality to shave another penny or two off the cost of production. Sure, more sectors means more chances for sector failures, but that does not explain why entire drives seem to be failing at greater rates.
My belief is based on some pretty solid circumstantial evidence, IMO. Back in 2011, both Seagate and WD cut their standard 5 year warranties down to 3 years and in many cases just 1 year. The "spin" used by the makers to explain these warranty cutbacks is pretty standard PR/marketing hype. But it does not take a savvy consumer to see the real reason - they simply no longer trust their cheaper (quality, not price) drives anymore.
ComputerWorld, December 2011:
Hard drive manufacturers slash warranty periods
