Nothing in the post you're replying to is about "is 2000 passkeys storable", it's about "if I have 2000 passkeys and I need to move between an Apple device and an Android device, do I need to establish a second set of 2000 passkeys"?
No, the majority will not. If through some miracles, passkeys gain sudden and wide adoption, there will be a day of reckoning come around the next mobile refreshment cycle, maybe earlier.
People break their phones. That is normal experience. Entirely unsupported by passkeys as they are today.
I'm actually surprised we didn't have more pushback for ubiquitous 2FA, as they have similar threat profile - i.e. addressing the tin-foil threats of cybersecurity aficionados, while entirely ignoring the common threats to real people, in particular the one of broken or lost mobile device.
Dunno why the downvotes, if you're willing to trust Apple or Google this is a good method for passkey usage. because your touchID/faceid/opticalid auth gate the keyring's on either of these vendors your passkey works without having to migrate them. EDIT: Also ANY device that you add to your iCloud has access to the passkeys you've made... it's a dream for secure access.
What happens when the user decides to move to an Android device, or even is suspended from Apple for a suspected breach of the terms of service, or Apple decides to not support their country anymore? There are countless reasons to prefer to manage one's own access.
Downvotes does not matter. People here that are privacy inclined always find ways to argue about Google or Apple (any major companies). But if you look at their private lives - they adopt tech ASAP. A majority have Apple Pay or Google Pay. Paypal. At the same time use bitwarden also. (And that is fine)
These privacy zealots fail to realise that majority of population does not have time to setup bitwarden server or lineageos or zfs storage etc.