The side effects aren't well known / understood. They also happen to less than 1% of people who take the drugs (at least that's the current estimate, some side effects may not be properly linked to the drugs). There's very little research on how to measure the damage done by fluoroquinolones. Once a patient says they have tingling, the drugs have already caused permanent damage, and a doctor isn't going to know what to measure to assess this damage, nor what they should have been measuring to prevent the side effect in the first place. This lack of understanding may lead to an inflated sense of safety profile.

They're used to treat antibiotic resistant infections in "hard to reach" places, since the fluorine moiety allows them to penetrate most places in the body (which is also likely related to how they cause insidious damage). This power+reach makes them a default drug for some doctors to treat infections.