In an informal letter, we write the sender's address Why is that so Why don't we write the - English - Informal Letter

Question

In an informal letter, we write the sender's address Why is that
so? Why don't we write the address of the person we're going to
send? After all the letter is going to them and not
us Please clarify

Nitika Sahdev · Accepted Answer

In an informal letter, the receiver's address is written on the
envelope and not as part of the letter Your own address is written
as a reference for the other person to reply to you

In an informal letter, we write the sender's address. Why is that so? Why don't we write the address of the person we're going to send? After all the letter is going to them and not us. Please clarify.