Solo: A Star Wars Story has done poorly at the box office, at least in regards to its reported $250-300 million budget. Indeed, one could argue that it was destined to fail due to behind-the-scenes problems, as well as general disinterest from fans.
As many now know, Solo was originally going to be directed by the filmmaking team of Phil Lord and Chris Miller, who were fired with about three weeks left in the scheduled filming. There were creative differences between them and the studio: while Disney and Lucasfilm apparently wanted a fairly typical Star Wars movie with a little extra humor, they reportedly tried to make a full-on sci-fi/comedy similar to The Guardians of the Galaxy.
They also favored an improvisational style that diverged from the script written by Lawrence and Jonathan Kasdan, and which caused the budget to go up. When they were replaced by Ron Howard, he was allowed to reshoot somewhere between 70-80% of the movie, which naturally increased the budget more. At this point, the powers that be were mostly just concerned with getting a good Star Wars movie out on time, but obviously the cost (highest of any film in the franchise) was going to make it harder to reach a profit.
According to Vulture.com, rumors of behind-the-scenes problems also made some skeptical of the movie, but to be fair, many already were before these issues were revealed. Many fans disliked the idea of a Han Solo standalone movie from the time that the idea was announced. There could be many reasons for this: the part is associated so closely with Harrison Ford that the idea of another actor doing it seems blasphemous, however good Alden Ehrenreich managed to be. Many also commented that the idea seemed unnecessary, as the movie is pretty much disconnected from any of the main “Trilogy” films.
Combined with poor marketing (which was delayed in part from the troubled production), Lucasfilm did not do a good job selling Solo as an “event;” unlike one of the “Episodes” or even Rogue One, this seemed like a movie that fans could skip, if they wanted to. Other factors came into play, such as heavy competition from Deadpool 2 and even Avengers: Infinity War, but high costs and general apathy may have been the main issues.