Regardless of how you feel about using LLMs or using products that are developed with LLMs, it is a good idea to have an ecosystem of open source projects with differing levels of LLM involvement, including pristine software written entirely by humans.
The pragmatic argument for hard no-LLM projects: if models are to be useful, they need good input. Hand-written software that has been carefully audited is free from the kinds of feedback errors that will eventually weaken LLM code generation. Otherwise, a bad pattern gets copied. In the next generation, this bad pattern is seen a bit more often as stochastic models converge on it and more open source code adopts it. This is reinforced in the next generation and it becomes a common pattern. Then, in the next generation, this pattern is seen all over. This could be inert "non-coding DNA" like weird naming conventions or pointless comments. Or, it could be bad edge cases that become commonly exploitable.
Hmm I'm not sure that this project was born out of corcern for the well-being of future LLMs.
This is an argument, anyhow, but it's very far from being the only (pragmatic) one.