Sodium-ion chemistry, material sourcing, and manufacturing techniques are still in flux. Longevity is still an issue. They're still a breakthrough innovation, not a solved problem.

As it turns out, capitalism is better at driving iteration than innovation. Research into groundbreaking tech is expensive, risky, and the benefits tend to be spread out over entire industries, so private investors find it difficult to capitalize on (read: privatize) the benefits.

There is still investment in optimizing NMC and LFP batteries not because "big lithium" has its hooks in people, but because low-risk patentable iterative improvement is all the private sector is really good for.

This is why, if you dig deep enough, almost every "world-changing" technology you use today has its roots in government research or grants -- microchips (US Air Force and NASA), accelerometers (Sandia Natl Labs, NASA), GPS (US DOD), touchscreens (Oak Ridge Natl Labs), the internet (ARPA), and even the lithium battery itself (NASA). The list goes on, and it gets particularly impressive when you look at medical breakthroughs.

Today, the US DOE has its net spread wide, funding dozens of different battery chemistries. Argonne Natl Lab is working on Na-ion right now, among others. For mostly political reasons, US-funded research doesn't "pick winners," so they won't ever truly go all-in on one tech.

TL;DR: Na-ion batteries are still a breakthrough technology, so expect funding/research from state actors like the DOE or CATL to push it over the line before the private-sector investment floodgates open.