Is there no privacy?

I'm open to understanding why spouses share an email address? My friend called it the "home email"; but it's the only email I have for her and it has her name in the address, not the family name. Why not just have your own email address and your spouse have his own? Why is it necessary to share an email? My husband and I do not, nor ever will, share an email address. It's not that I'm sending secret messages to my secret lover (we sneak late night phone calls instead) and don't want my husband to find out, I just want some things to be my own. Is it because you don't check email that often and people are scheduling playdates via email? Okay, I get that. Then, why not still have your own private email? Is it too much to check? I just don't get it.