WBS license IP from Warner Bros Productions (WBP).
WBS hire sets and costumes from WBP.
WBS pays WBP for promotional marketing.
All workers are contracted with WBS, who is making the movie.
Movie brings in millions or billions in revenue to WBS.
It just so happens that all those things, IP, sets, costumes, marketing, well they all came to more millions and billions, which WBS now needs to pay WBP.
WBS operates at a loss, WBP gets all the profits.
The reality is much more complicated than that, but that’s the gist of it - and the Hollywood entertainment industry aren’t the only ones doing it anymore.