I am offering this houserule because they are put off by attack rolls anyway, they get jumpy and throw the dice across the table and then they get socially awkward. They wouldn't chose to use a crossbow, especially as they as individuals have aversions to weapons, but not spells. It's a personal preference. They think spells are cool, they don't think swords and bows and guns are cool.
Though they can of course change their mind
They may decide one day "I'm gonna use a crossbow, I've changed my mind" but they're not FORCED to. They always have the option to depend on Eldritch Blast.
Particularly, even if forced into close combat, they are going to tell if a melee character refuses to close within 5ft of them just so they aren't in the position where EB is ineffective and they have to use a dagger or something.
EB being ineffective because it's a spell attack, different if it's a dexterity save.
They may chose a warlock spell that has a spell attack, but there's only 4 warlock spells that have a ranged spell attack. One of them is Witch Bolt which is a notoriously bad spell that I'd recommend they not take