HPV is the most common cause of abnormal pap smears.
It is only fairly recently that we get more specific results with pap smears, telling us whether an ‘abnormal’ finding is related to a low-risk or high-risk HPV type. If it’s low-risk, we treat it like a normal pap smear, with a recommended annual test. High-risk HPV requires further follow-up, typically a colposcopy and possibly a biopsy. (Don't be alarmed by "colposcopy," by the way. I know it's a scary word, but it only means using a bright light and magnification to inspect the cervix.)
These more advanced pap smears, by telling us more about the HPV, save many women the inconvenience, cost, and discomfort of those further tests.
We’re not sure why women develop an abnormal pap smear 10 to 15 years after an initial exposure to an HPV type. It probably has to do with the viral type of HPV (remember most are low risk), your immune system, and other factors we don’t know. A new ‘abnormal’ pap smear result is not evidence that you have been re-infected. If you have been with the same partner, had an occasional abnormal pap, but nothing has progressed significantly, you are unlikely to have an aggressive, high-risk HPV type.