Using 10-10s to call internationally can be a bargain if you are careful about monthly fees, ... Many of the pre-subscribed international calling plans offered to residential customers by primary carriers have somewhat higher rates and charge a monthly fee.
They can be tempting but they have very, very high interest rates, ... you pay as you go.
The factors cited by card issuers are very broad. It appears that anyone - not just people in financial difficulties - could be subjected to a much higher rate for very insignificant reasons.