Doing end-to-end cryptography is hard enough to get right. Adding multiple devices to the mix makes it even harder.
So it's an explicit trade-off, made to keep your communication safer. Signal, in general, is uncompromising about privacy and about keeping metadata out of their hands.
YMMV and it's always down to threat model... absurd ammount of information is sent via plain text email
in case of XMPP you have OMEMO which is multi device and works fine-ish (nowadays) though I would still prefer simpler OX (PGP; pefrect-forward-secrecy is an overkill IMHO for majority of people)
just means more places to get your key stolen from.
Just don't talk so nobody will steal your communications.