There is no need for some BTC wallet developer to focus on implementing other coins which the majority of electrum user simply does not need.
it wouldn't take that much focus though specially if the developer of such wallets focused mainly on copy coins such as litecoin or even less obvious ones. the similarities between different cryptocurrencies are so much that makes writing most parts of a the wallet trivial.
i agree that Electrum will never and should never do it because it is a bitcoin focused wallet.