In mass scenarios, service call overhead can become prohibitive and tedious, and remote communication overhead can take longer (up to 10x) than executing the rules.
When bandwidth is limited or if the network is unstable, local execution becomes ideal. In mobile setups, network reliability is an important aspect.
Sending critical data via network can be avoided by enterprises by executing the rules locally for better regulatory compliance (PCI, SOX).
By removing dependency on other systems, it avoids a single point of failure. For example, maintenance of the SAP back-end should not take down the e-commerce platform.