I think in-universe you are trying to keep the environment in balance but it's so hard to make a good story for a game exclusively about killing and wearing monsters that it never works out.
Iceborne ends with the main characters thanking Nergigante only for that particular Nergigante to be the target of a future hunt regardless.
The questlines are so intuitive that some were missing an ending for a few months due to bugs and nobody noticed.