Originally Posted by
intuition
Yeah, the rule doesn't really make sense for AY, since they serve only a limited number of destinations on their own. They serve several major OW hubs, but there are IMO very few codesahares in general, and some of the codeshares can't even be booked IRL (at least not on AY web page, maybe a TA can).
You don't need to be on a codeshare to book the trip on a single ticket. E.g. to TPE you can buy a ticket from AY with HEL - HKG on AY and HKG - TPE on CX. They same applies to a number of CX destinations which don't have AY codeshares. In the end being not able to buy a single ticket is a marginal case when connecting through OW hubs, so AY must have calculated that they will get more revenue by encouraging people to buy their trips on a single ticket.