There Are Policies Against Dating Passengers
Many flight attendants will tell you there is no policy against them dating passengers. However, an implicit code prohibits employees from socializing too much with passengers. That is a valid reason to decline interested passengers courteously.
We can only imagine the constant stream of attention they receive from their passengers. This unstated rule is to their advantage unless they are also interested, in which case you can exchange contact information; Don’t hold your breath for it to happen, though.