Because Boltz swaps are non-custodial, every seemingly one-way transactions actually consists of two transactions: lockup and claim. See my basic explanation of how atomic swaps work above: #339303. Meaning, for chain to Lightning swaps the user is already paying for sending aka locking the funds like you said but still needs to pay for Boltz claiming the funds. That's why the charged network fees here are roughly half of the other direction.

So Atomic swaps always have a higher chain footprint than custodial swaps, because they require two transactions instead of one. But we are convinced 100% non-custodial is the only way forward, we think Liquid is really handy where network fees are low.

We are constantly monitoring and looking very closely before we decide to integrate swaps for a new layer. In general we move rather slow with this. We carefully evaluate adoption, soundness security-wise and verifiable 1:1 mainchain backing is also a requirement.