The idea is, once the main address receives a tx, it changes further encouraging anonymous transactions. Old addresses are still valid but not showing up in the wallet to keep users from ruining their privacy with laziness.
As soon as you use an address, it's no longer anonymous, since it can be traced.And reusing address just makes it way more easier to figure out who's using it.
Reminds me of IOTA. But hopefully with none of the attendant issues.
Can't test the changing address feature yet since it is not possible to send or receive a tx on the main wallet address so no idea if it does not show up in the wallet after a tx has been received.