Solo’s biggest issue was that they (bafflingly) placed it in May rather than December, just six months after the last movie. Then they failed to properly market the movie at all. They failed to give it an original “feel” (love or hate it, the MCU does a really good job making each trailer feel unique so people hype about each movie). Last, and most of all, it was right after Infinity War AND Deadpool 2. Movies that to the general audience were far more interesting than a Solo origin movie.