I'm not entirely sure specifically as there could be many different 'princess guard archon visual novels'. Generally, it might involve a story about a guard protecting a princess in a world with archon - related elements, perhaps with elements of fantasy, adventure and character relationships.
One aspect of Vegito and Female Gogeta fanfiction could be the exploration of their unique power combinations. In these fanfictions, writers might create scenarios where they team up against a powerful enemy. For example, they could face a new, extremely strong villain that neither could defeat alone. Their combined strength and different fighting styles would make for an exciting story.
There is 'Archon's Quest'. This light novel is full of adventures. The world - building in it is quite fascinating, making the readers feel as if they are in the story. It follows the journey of the main character in an archon - filled world.
One common theme is power comparison. Writers often explore how Vegito's power from Dragon Ball stacks up against the powers in the other crossover universe, like the magic in a Harry Potter crossover or the quirks in a My Hero Academia crossover.
Maybe it's because Bulma has her own established character traits and relationships in the original story. She might not fit well into the scenarios often presented in Vegito fanfic. Also, her character is more focused on other aspects like her scientific work and family in the canon, so fanfic ideas involving her in a Vegito - related context could seem out of place to her character.
If Vegito never unfused, it might mean that the enemies he faced were simply not strong enough to force the separation. This could imply that the story's difficulty level was lower than originally thought. Or, it could be that some external factor prevented the unfusing, creating a whole new set of plot twists and complications.
You can try looking for it on popular visual novel platforms like Steam. Sometimes, smaller indie visual novel websites also host such works. Just make sure to check the reviews and ratings before downloading.
One reason could be that the fanfic might distort her character. Bulma is a smart scientist, and if the Vegito fanfic makes her act in a way that's not true to her intelligent and rational self, she would seem to reject it. For instance, if the fanfic has her being overly emotional or doing things that are completely against her scientific nature just to fit into a Vegito - centered plot.