Generic Routing Encapsulation (GRE) is designed to encapsulate a wide variety of network layer protocols for routing over IP networks, making it ideal for situations where a VPN must carry different types of traffic without the need for encryption. GRE supports broadcasting and multicasting, and can encapsulate a variety of network layer protocols, which perfectly fits the requirement of the scenario. In contrast, PPTP is limited and doesn't support the encapsulation of a broad range of network protocols, and while L2TP and IPSec are VPN protocols that could encapsulate different protocols, they primarily focus on security and encryption, which isn't a requirement in the given scenario.