I never understood why they don't support the subsonic protocol.
I mean... you might as well ask why the DLNA plugin has been broken for years. Or why they don't add a custom HTTP header to the client app so people can lock access in their reverse proxy.
As usual it's a mix of not enough developer manpower and "I don't use that so it's not a priority" i.e. the whimsies of FOSS.
Or sync to a local directory and slap Dovecot+Roundcube on top, and you have your own private searchable email archive you can use indefinitely/securely/remotely. Just update imapsync to pull from the new provider when you switch.