Date of birth

Why do they need my date of birth for a competition entry? Isn't it enough that they have my name, email address, phone number, physical address and ... well, I'm sure there was something else they needed before they would let me submit my competition entry. Bad enough they now have all my marketing information without making it easier for them to identify me. I can't help but wonder how secure their digital and cloud information and databases are, but I guess for the prize - a $21,000 cruise, it's worth a go.