Movies have a sequel problem. Whenever a film is successful enough, the studios and executives behind its creation will always want to milk the movie's profitability as much as possible. Consequently, this practice will often lead to a slew of unnecessary sequels that diminish the legacy of the initial film. However, despite the quality of these sequels, fans of the original movie will usually turn up on opening day simply because they want to keep exploring the characters they love.
The truth is that people who fall in love with a fictional world usually want to remain immersed in it for years. A film with a finite run time, irrespective of its quality, is limited to the amount of immersion it can offer viewers. In contrast, a video game based on the world of the film allows fans to prolong their enjoyment without engaging with a shameless, cash-grab sequel.
Luckily, Studio Ghibli films haven't produced any useless sequels but have also traditionally abstained from creating peripheral content for fans that enjoy the story worlds they weave. What would a series of Studio Ghibli games look like? In the post linked above, you can check out some cool fan art that answers that exact question.