Making your traffic cross jurisdictional boundaries also adds a level of difficulty for tracking usage.

Local law enforcement can tap a local ISP for their records, but it would take a scale more effort to then tap a non-local service provider for their records. Each additional level of difficulty adds a cost, and at some point those costs aren't worth the potential results.

(assuming that the VPN provider doesn't just roll over due to an email inquiry, or isn't a front for very cooperative law enforcement).