How do you game it apart from stealing a phone? It may be easy to get another identity but that's a feature.
If somebody commits a serious crime, the joined location of the phones will reveal the true identity unless somebody invests an amount of effort that's equal to buying a new passport.
So you get several identities. How do you game the system?
Intelligent agencies have failed to keep their phone usage cleanly separated. It's not that easy.
E.g. if you want to avoid progressive income taxes by registering several companies, your burner phone stands out because it doesn't have any other contacts. That will be further investigated.
Then you need the name of a living person who doesn't use a mobile phone to register it because otherwise, he would operate two phones at two different places. Another red flag.
If somebody commits a serious crime, the joined location of the phones will reveal the true identity unless somebody invests an amount of effort that's equal to buying a new passport.