Because it's an alias you can't "log into it" so to speak. You would log into iCloud like normal, and when you go to mail just choose to send it from your @me.com address.How can we even login with me.com, they changed it to iCloud.com a while ago? Yeah, I thought it was just an alias as well.
For a while i thought they were separate, and i rarely used them.. for security reasons i would have liked to change the pass, which failed hard. Only to realise it's an alias. I don't know why I didn't even consider that. I am so used to managing my own email at my server at home. Or just use my public one from gmail.. that it perhaps didn't even occur to me.