EV manufacturers have been searching for ways to make better/cheaper/denser batteries, not better/cheaper/denser lithium batteries.
Sure, it’s the lithium battery manufacturers that are invested in making better lithium batteries. Everyone has been buying their products for decades and they want that to keep happening, so they pour resources into research and development. And they have a lot of resources, because everyone has been buying their products.
Once a market settles on a particular technology it becomes self-feeding and tends to accelerate. It’s difficult for a competing technology to break in primarily because of momentum - it’s hard to catch up.
A device manufacturer might be interested in using a different battery technology, but if they have a whole design and production process already built around lithium batteries then it’s not just the battery that they have to change. It’s their logistics chain, on-device electronics, design theory and possible regulatory concerns. Changing an established system is expensive, so that has to be justified somehow.
I’m not saying that it can’t happen - I’m sure that it will eventually. What I’m saying is that in order for a different battery technology to really change the market and push lithium out, it will have to be significantly better (not just marginally better).