The concept gets stretched to its absolute limit in those fics, which is kind of the point. It's rarely just about getting money; it's a narrative key to unlock power, political legitimacy, and, most importantly, the justification for the harem structure itself. The most common trope I've seen is the 'Black Family Inheritance,' where Harry discovers he's the last heir or a secondary heir to the 'Most Ancient and Noble House of Black.' The Gringotts goblins present him with a list of betrothal contracts or 'alliance obligations' tied to the title—suddenly, he's magically bound to marry Daphne Greengrass, Susan Bones, Fleur Delacour, maybe even a Black cousin like Bellatrix or Narcissa if time travel is involved. It's a convenient, in-universe legal framework to sidestep the usual romance buildup.
Honestly, the portrayal swings between wish-fulfillment power fantasy and surprisingly intricate world-building. In the weaker stories, inheritance is a blunt instrument: Harry takes a test, gets a dozen titles, and now every witch is magically compelled to be with him. It can feel cheap. But I've read a few where the author actually treats it like a burden—ancient magics demanding he rebuild a fallen house, with political marriages as a necessary, sometimes grim, component. The harem becomes less about indulgence and more about managing a web of alliances, with each relationship serving a different strategic purpose for the 'House of Potter-Black-Gryffindor-Slytherin-Whatever.' The magic itself is often portrayed as sentient or contractual, enforcing the bonds whether the characters initially want them or not, which creates its own kind of drama. I keep reading them for the rare ones that lean into that gothic, political complexity instead of just the smut.