Upvote:4
TL;DR: It's complicated.
Here's the baseline scenario: Flights from A via B to C, operated by airlines 1 and 2. If you buy a ticket from A to B, airline 1 gets all the money; if you buy a separate ticket from B to C, airline 2 gets all the money.
To merge the two as a connecting A-B-C flight, there are three basic options:
Upvote:5
There is no "extra money". The BHX-FRA-WDH fare is priced as a single entity and represents just one of many different fares sold for any particular flight. No single fare class represents "The Fare" for that flight, they are all calculated using formulas that are designed to: fill the plane, cover costs of operations and make a profit.
So they aren't charging you more because they provide something extra, they are charging you more because that ticket falls into a different (more expensive) fare basis. With a few exceptions, a seat in economy gets the same services irregardless of what price you paid.
jpatokal covered the basic methods of revenue distribution, but for that flight the revenue is based on what Lufthansa's and Air Namibia's prices are for that particular fare class. The fact that other lower prices are offered on the same flight does not come into play when calculating revenue distribution for that particular ticket.