When a classmate joins it looks like they have to re-enter information that is already in their profile such as email address, street address etc. Why is that, or do I have something set up wrong?

It's just a failsafe. In my cases the email address and/or street address you have for somebody is no longer valid. We could pre populate those fields, yes, but that just gives the registrant room for error. E.G. If they're not prompted to enter something, they could potentially leave the default which is wrong. By asking the new member for current contact info and making them type it in, you're assured of getting current contact info. Simple as that.

Except when they delete it.

They can't actually delete either one. The Classmate has to enter an email address because email address serves as login address. So while they could delete the original email address provided by the Administrator, they could only do so by replacing it with a more current address.

If they leave the street address, city, or state fields, blank, the original information entered by the Admin is retained in the system and also used on the Excel export feature (in case you are sending out something in the regular mail to Classmates).