My guess is Siemens is going for it because if you can get the load/generation balancing right, it costs much less than hardening. Might also be more resilient. Only way to fully harden these systems is underground them at 10 (100?) times the cost.
There's also probably some research funding provided by DOE for this because it's a new approach. And if it works, it would be beneficial in tons of other places.
Also worth noting that even if you put them underground, you could flood your tunnels, or have an earthquake, or a giant rabid mole attack, etc...
I don't read your comment as ignoring this, but I want to point out for everyone that reliability always has tradeoffs about what events you want to be able to handle and how much preparation you want to do / pay someone to do for you.
Our (german) underground cables are waterproof and bite-proof, the latter to varying degrees.
Earthquakes are an issue, but iirc they only tend to require a few splices, not a new cable.
There's also probably some research funding provided by DOE for this because it's a new approach. And if it works, it would be beneficial in tons of other places.