Localising Japanese games for western release is a costly process, and even today we still see a lot of titles remaining Japan exclusives and therefore tantalisingly out of reach. Back in the '90s it was very much the same deal, with many amazing 16-bit games failing to make the jump to the west.
Amazingly, Treasure's sublime Gunstar Heroes was almost one of those titles. According to former Sega of America producer Mac Senour, the game only saw release in the US because he fell in love with it after every other producer turned it down:
Not just all the producers, all of the associate producers as well. 12 people looked at it and passed before it got to me. If I didn’t pick it up, he was going to be rejected. I played it for five minutes, maybe less, and threw the controller on the floor and said “this is game of the year.” Every one in earshot laughed.
The reason was made very clear to me. Gunstar had small characters. We had just published, or were about to publish, World Series Baseball with a HUGE batter. All the games were showing off something the developers of Spider-Man had discovered, a way to make double high sprites. Gunstar didn’t use this and so the others passed. I saw it as something different. I have to say I made only one real change: there’s a boss in a military uniform, and in the original version he was Hitler. I asked them to remove the moustache or change the character.
Gunstar Heroes also saw release in Europe, but had the US launch not happened, there's a good chance that the game would have skipped that region, too. Seems like Sega fans all over the world owe Senour a massive Thank You!