It really doesn't strike me as amazing that it's still prescribed, Mark. It's an extremely effective antibiotic, particularly for urinary tract infections, and the overwhelming majority of people have no problems with it. I've been prescribed it many times myself and it's always worked well for me.
Now that you know you're allergic to it you can ask for an alternative, but it would be a case of throwing the baby out with the bath water to stop prescribing such an effective drug because of a small number of allergies.
Cheers,
Chris