Why doesn't Ethereum core developers work on zk proofs?

Sorry if this question may sound stupid.

Vitalik Butterin said that "in the medium to long term ZK rollups will win out in all use cases as ZK-SNARK technology improves." (https://vitalik.ca/general/2021/01/05/rollup.html#conclusion). It means that he truly believes in the power of zk proofs technology. He thinks that they may be the best answer to scale Ethereum. So, instead of just "watching" other teams working on it, why don't Ethereum core developers work on a such implementation?

• Is it because they need to focus on the move to Ethereum 2.0 ?
• Is it because the true nature of L1 is different from the nature of L2, in terms of ethos, principles, vision, etc. ? And so they would just prefer to focus on other things?
• ...

Thanks!