They are exported so you can sync to a Denon device, where they do work. Not syncing them means you could lose them and that’s probably not what you want.
Yeah that is a better way. It’s silly Engine desktop doesn’t support streaming tracks yet, that would solve it. I’m sure they will support it at some point.
Not exporting streaming tracks to Engine desktop would cause the problem that your playlists would become inaccurate (normal tracks synced, streaming tracks skipped). If you then re-import that playlist, streaming tracks would be gone from Lexicon too.