Kind of a long post, bear with me. I've actually been very interested in this topic for years.
I don't know if it's actually been said yet, but the original reason that circumcision was introduced to the United States was not hygiene. Due to Victorian Era values and spotty medical science, masturbation was believed to be the root of many ailments. Most of the old wives' tales about the consequences of masturbation (such as hairy palms, blindness and acne) are remnants of an era when such things were accepted as medical fact. Thus, doctors perceived it as helpful to the general health of the populace to try to take measures to restrict masturbation, and the easiest way they thought to do so was through reducing the amount of pleasure received from the process by limiting skin mobility. (for those that have taken a psychology course, this is an example of positive punishment) It is also noteworthy that religious reasons motivated much of Victorian Era science, as evidenced by the two main spokesmen who convinced the American Medical Association to standardize and push the procedure were a priest and a rabbi (I wish I were kidding). Some products came about from the belief that masturbation was harmful as well. Graham crackers, so named because they were invented by a man named Graham, were created because science believed a mild diet would reduce sex drive, and hence the desire to masturbate.
Now that the origin's been discussed, the better question is: Why has the practice of circumcision persisted in the US as long as it has? The answer to that is, unfortunately, a business one. While not a hefty amount, circumcision procedures do cost money, and hence are a source of income to hospitals and doctors. While any good business is open to the possibility of new procedures or activities that can increase income, they will tend to resist change that will decrease it, and they may try to find reasons to keep the existing procedures in place. After all, a circumcision is fast, easy, and contributes money to the hospital. While the doctor may prefer to be taking a nap, the hospital schedules the procedures unless he has a private practice. They want to keep any revenue that is available to them.
This of course meant that when it was proven that masturbation was not linked to any of the diseases it was believed to cause, doctors needed a new reason to justify the procedure. Many speculated that because UTIs could be caused by foreskin complications, such as phimosis, it was better to remove it at birth in order to prevent such occurrences. This was not based off medical research, it was merely assumed that any uncircumcised child with a UTI received it because of his foreskin. This gave them a continued reason to perform their procedure.
Of course, the biggest cause of contracting a UTI is lack of hygiene. Doctors often speculated that, because the infant's foreskin had to be forcibly retracted in order to clean the glans of the penis, it made proper bathing more difficult, and cause the UTIs. This point of view was mainly caused by the lack of pediatric medical science, so in many ways children were thought of as small adults physically. The child's foreskin is actually attached to the glans because it protects the penis from exposure to filth (read: diaper crap) which may cause an infection, in some ways serving as the equivalent of a hymen for males. It naturally separates later in life to allow for sexual skin mobility and to prepare the child for sexually maturity. Forcing the skin back prematurely is painful, but can happen, much like breaking a hymen. However, the mucocutaneous tissue of the inside of the foreskin is self regulating, and actually keeps the penis fairly clean on its own. Ironically, by removing the protective functions of the foreskin and simulataneously creating incisions in the penis, doctors were often causing the very UTIs they sought to prevent.
Now the American Medical Association has reversed it's stance on RIC (sometime around 2004 or 2005 I believe) and encourage parents to not circumcise their infants, stating that it is an ineffective procedure in the prevention of UTIs and other complications. They avoid the obvious arguments of the morality or ethical arguments, but it is what it is. Although they have changed their position, many parents will still continue to circumcise their infants because of tradition. If it's good enough for Daddy, it's good enough for Junior. Changing of tradition requires recognition that one way is better than the status quo, and in this situation, it requires the fathers to admit to themselves that a very personal part of their anatomy was needlessly removed from them without their consent. Many men are unwilling to do this, either because our culture discourages men from decrying themselves as victims or because, having never had a foreskin they can remember, they are not aware of the difference. Eventually attitudes will change, but they just need to be "grandfathered" in so to speak. All in good time.