Lucas may have been physically vulnerable according to where he was & what he was doing (nobility that travel without an entourage are at greater risk). However, he's not vulnerable in the fact that a lot of high-powered people will miss him & come looking for him, making the kidnapper more vulnerable to retribution.
"Cute and vulnerable" seems to explain a large number of kidnappings in this comic.
Lucas may have been physically vulnerable according to where he was & what he was doing (nobility that travel without an entourage are at greater risk). However, he's not vulnerable in the fact that a lot of high-powered people will miss him & come looking for him, making the kidnapper more vulnerable to retribution.