Why doesn't AOL REPLY and FORWARD retain the previous email thread?
Because they are deliberately trying to reduce the load on their servers, both AOL and other web based email systems consistently choose not to follow common standards and practices of the rest of the internet world. They do not include the prior message when replying. And, they do not provide a way for the user to change that default.
How AOL Users Can Include Prior Email
To include the prior email in an AOL email reply:
1. "Select" all of the email you are replying to, either with your mouse or by placing the cursor in that email and typing Ctrl-A;
2. Then, after selecting all of this email, click to reply.
If you do it in this sequence, AOL will include the prior email in your reply.