Presumably the SIMs were anonymously bought/registered. There's no link to the user. If you knew the drug kingpin was using a particular sim/phone (IMSI/IEMI), you can track it, but that's like looking for a needle in a haystack (no intercepted texts/calls to go by).
If you know two locations that the kingpin in question frequents regularly (for most of us that is home & work), you can easily narrow down your haystack down to very few needles real fast. How many people live within 50m of your home and work within 50m of your office?
