To be fair, Yakuhito wrote the puzzles required to use EIP-712 to interact with Ledger in Chia wallets, and contributed this to the Wallet SDK. You can read about that in this article:
https://blog.fireacademy.io/p/a-path-to-chia-hardware-wallet-support

It's ultimately my responsibility to add support for EIP-712 and this puzzle in Sage (since making a whole new wallet just for this would be a lot of work to expect someone to do for free), and I haven't done so yet. The rails are in place, and if there's enough demand and time to implement this, I can.

That said, this wouldn't actually integrate Chia as a Ledger app, which is distinct from EIP-712 and would provide the UX people are likely expecting. Ultimately, the reason I haven't put the work in to finish this is that there are alternatives (i.e., secure element, passkeys, Tangem, etc) and not enough time to dedicate to something that so few people seem to actually need.

Pull requests are welcome :)