Why would a player drawn to spellcasters prefer weapon attacks over cantrips? I think that's the question we need to focus on.
Are they having trouble finding spells that fit the theme of their character? If so, maybe they'd benefit from looking at a wider range of source books. You can also remind them that they can "reflavor" their spells to better fit their character.
Is it utility magic that draws them to spellcasters? Are they even choosing offensive spells to begin with? If not, maybe you can help them out with a magic item - something to guarantee that they have access to a spell or two that would benefit the party. You could also shift some of the danger towards non-combat encounters to give their spells more value. For what it's worth I don't think there's anything wrong with utility-focused characters - they just tend not to shine as much in one-shots. Maybe if they knew more about the adventure ahead of time, they could better cater their character to the situations they're likely to face.
Are they overwhelmed by their character sheet? If so, playing short campaigns starting from level 1 might help to ease them into their class abilities. Spell cards might also be helpful if you're playing tabletop.