What is "not efficient enough"?
As a first guess, one would think it makes more sense to eat 30% loss (so you need 1/0.7=143% installed capacity) than to need 200% capacity plus batteries since it's night about half the time on average. And afaik HVDC is more on the order of ~15% loss
Aside from the physics, HVDC doesn't compete successfully on cost. It's cheaper to overbuild PV and use batteries.
... aside from the physics? What factors into this cost calculation other than the physics of solar panels, batteries, and cables?
Infrastructure (heck, just the conversion points alone are a huge part of the cost), but also regulatory hurdles like getting rights-of-way. Running an HVDC line is quite expensive; last time I saw the numbers crunched, it was basically impossible to make it work financially, no matter how efficient the lines were.