IApplication::FindExtensionByName does not return any results.
Prior to version 9.0, application extensions are always loaded during startup. At version 9.0, the concept of a just-in-time (JIT) extension is introduced to shorten application startup time by loading extensions only when they are required.
A number of extensions shipped with ArcGIS Desktop have been converted to JIT extensions since version 9.0. Both standard and JIT extensions can be obtained programmatically by calling IApplication::FindExtensionByCLSID or IApplication::FindExtensionByName. While FindExtensionByCLSID works reliably, FindExtensionByName only works with the following JIT extensions: