"Mai" is "never," so shouldn't the answer be "How come you never have a purse?" instead?
No: "come mai" is purely idiomatic and can be translated as "how come". If you were to translate "How come you never have a purse?" it'd be "Come mai non hai mai un borsellino?".
Thanks a lot! How would you say "How come you have a purse?", that is, with a positive premise?
It is pointed out - if you hover over it and get a "you peeked". What they need is a phrase vocabulary, so that it introduces special or idiomatic combinations of words such as this.
"How is it that" is better English than "How come". Should not be marked wrong.
my question is about borsellino. I understand the 'ion' to be a diminutive, but why wouldn't 'how come you don't have a small (or little) purse'?
It's actually a double diminutive: borsa (bag, from the Greek byrsa, leather) was diminished to borsello to refer to a little bag (not only to carry money) and then to borsellino with the modern meaning of purse. Borsello is now mostly disused. Note that purse comes from bursa too, but in English it's had the borsello/borsellino meaning from the start (Old English pursa).