Well, for one thing, Jacen Solo is a well - known character in the Star Wars universe. When he turns to the dark side, it creates a lot of opportunities for fanfic writers. They can explore his relationships in a new light. His friends and family now have to deal with him as an enemy. Also, the dark side often brings new and exciting powers and abilities, and seeing how Jacen uses these is very appealing. In addition, it allows for a deeper exploration of the Star Wars universe's concept of the dark side, like how it corrupts and what can be done to resist it.
Yes, he was, although his presence was not as prominent as in other Star Wars movies. 'Solo: A Star Wars Story' was centered around Han Solo's backstory. Darth Vader is a key figure in the Star Wars franchise, and while his character wasn't directly involved in the main plot of 'Solo', his existence in the Star Wars lore added a sense of the overarching dark side presence in the galaxy during that time period. The movie was mainly about Solo's journey, his relationships, and his entry into the seedy underbelly of the Star Wars universe, and Vader's character was not directly related to those aspects but was still part of the larger Star Wars context.
Darth Maul's appearance adds an element of surprise and ties into the broader Star Wars lore. It creates a connection to previous events and expands the narrative.
Darth Maul's appearance in Solo added an element of surprise and connected to the broader Star Wars universe. It was a strategic decision to expand his story and engage fans.