There is, you can only access them on the devices you sent them from or receive them from. If you add another client weeks down the line, you cannot access these messages anymore
not entirely true... you can pair a new device which shares the decryption key. hell, you could even do a p2p sync so the server stores nothing... there are plenty of options that get technically harder with each increment (perfect forward secrecy gives you some limitations), but you can absolutely backup and restore, or even live sync conversations between multiple devices even if it’s e2e
