I am a little surprised that handball has not taken off in the United States. It is very similar to racquetball and I would think that many people who enjoy that sport would carry over to handball. On reason may be the lack of facilities to participate in handball. The popularity of racquetball may also be one reason there is not as much interest in handball.
In addition to the very good points the previous posters have made, I would like to add another factor for consideration. Handball is not a sport seen in most schools in the United States. Limited financial resources in many areas keep the primary focus on football, basketball, baseball, and volleyball. Much of today's youth are growing up without learning even the most rudimentary things about this sport. They consequently become young adults with no knowledge or interest in this sport.
Handball doesn't get national attention through television viewing audiences. It is a sport that may be played in an elementary or high school gym class, but that is about the extent of exposure for most Americans. It is even an Olympic sport, but gets little to no coverage then. As post 2 mentions, Americans have so many other sports to choose from, many of which have aspects of handball, that they are likely to stick with what is popular in their area. Popularity of "new" sports starts with the youth and grows from there, so I think the only way to bring attention to the sport is to start offering organized intructional leagues to young people through schools or park district-type programming. I can attest that in my community, lacrosse has grown greatly in the past three or four years through this type of activity.
I think it's just because of tradition. I think the only reason Americans don't like the game is because it's not something they're used to. After all, it should be pretty compatible with American interests. It's fast-paced. The players use their hands. It's easy to understand -- after all, it's throwing a ball into a goal. All that says to me that it's just a matter of what's traditional.
I think it would be hard to get people very interested because there are so many choices for us in terms of what we can play or watch. In order for handball to become more popular it would have to push something else out. That's awfully tough to do.