Why not claimable balances
A claimable balance is the Stellar way to pay someone who is not there yet. Sown cannot use it for the people it is for.
Only a classic Stellar account can claim a claimable balance, and the person Sown most needs to reach has no account at all. Their new wallet is a passkey smart account: a contract, which cannot claim one.
A classic payment cannot go to a contract address either, and it cannot write the receipt. So the envelope is a contract entry: the smart-account-era claimable balance, with the keep bought inside the same transaction and the receipt written beside it.
For someone who already has a classic wallet, a native claimable-balance path is on the roadmap.
Next: What the issuer can do