Should I mention in statement of purpose that my undergrad degree is in a different field because my parents wanted me to do it? Is it okay to mention in my statement of purpose for admission to grad school in math, that my undergraduate major is engineering because my parents wanted me to do it? 

I was initially wrote my statement without including my motivation for undergraduate degree, however people said it seemed too abrupt. However, without it, I'm not sure how to tell why despite being interested in math, I still chose engineering as a major. 

EDIT: Thank you for your responses, I should mention that, after my undergrad degree, I have managed to enrol in one of the top masters program in math in my country and I'm doing well there, and also that there was not really any scope to learn pure math in my undergrad university.
Do not say: 


  "I did engineering undergraduate because my parents made me."


Why?
Because you are applying for graduate school. The admissions committee wants to see adults. Referring to your parents (at all) makes it seem like you are not independent -- that your parents run your life. Whether or not they do, it does not benefit you to give such an impression. You don't want to put the idea in their heads, whether or not it is true now (or then).

I suggest, if your really must mention it at all, something along the lines of: 


  "My time as a Engineering undergraduate has made clear to me my true desires. While engineering is a interesting and worthy subject, my passion is for mathematical side I saw during my studies."