Accessible keys are a security risk, regardless of how you feel about it. If a key is accessible on the system then any exploit with elevated read permissions can steal the entire key store. By leveraging hardware features that let you add and use a key but prevent reading it, you mitigate that risk. There’s a reason that on Yubikeys, secrets are write-only.

Bitwarden, 1Password, and other companies who build password managers are able to operate with higher expectations of their users. Their users opted into using a flexible, secure tool, and as such, they can provide riskier options to their customers. They know that providing a TOTP solution in their application doesn’t force their customers to use it when doing so would be outside their risk tolerance.

That said, every password manager that I know of - Apple’s, Google’s, Microsoft’s, Firefox’s, as well as dedicated password managers - has an export tool. But this doesn’t mean that all of those providers value having flexibility. I’d argue that in many cases it just means that they recognize that a password alone isn’t trusted enough to warrant concealing it. Given that you have to know the password to enter it, there’s much less value in concealing it from the end user. Since passkeys don’t work that way and do have that value, it makes sense for providers, if they are opting to prioritize security, would choose a less-flexible solution that most of their users don’t care about.

If the big providers did offer a more flexible alternative, enabling exports, to advanced users, those users would necessarily have reduced security and they would have to opt into that ahead of time, since later the secrets would be inaccessible (theoretically - depending on how the syncing is implemented it might be feasible to intercept them. My assumption, since syncing is within a given ecosystem only, is that when synced they are encrypted with a public key that only their secure hardware can decrypt). Also, having such an option would require a different code pathway when interacting with the secrets store, which would mean more potential code that could have bugs.