Originally Posted by
Lux Flyer
The joint-venture has more to do with setting flight schedules, revenue sharing for TATL segments and making seats available to one another via codeshare. It is a collaboration among competitors, but one of the things they can't do is collude on setting fares, as that would be easily shown to be anti-competitive and regulators would be all over that and shut the joint-venture down.
As
findark said, perhaps a bit more obliquely, this is entirely inaccurate. The JV specifically
does allow them to collaborate on setting fares, which is why UA and LH fares are always identical in the JV markets.* JVs have to be approved by all involved governments, and they include immunization from antitrust prosecution for specifically this kind of thing.
You may be thinking of a simple codeshare agreement, which is a more limited immunization that does not allow for collaboration on fares.
If they also wanted to collaborate on inventory values, I don't see any legal reason that they couldn't do so. I suspect that they've decided not to do so because each wants their own revenue management team to have complete control over the inventory under their codes.
* ETA: For anyone who's not following -- the price is a combination of the filed fare and the bucket inventory. So
prices can differ even though the
fares do not.