Because does not participate compiling
UnrealEngine4 use metadata parsed by the Unreal Header Tool keyword UPROPERTY(…) get member define info.
// These macros wrap metadata parsed by the Unreal Header Tool, and are otherwise
// ignored when code containing them is compiled by the C++ compiler
#define UPROPERTY(…)
#define UFUNCTION(…)
#define USTRUCT(…)
#define UMETA(…)
#define UPARAM(…)
#define UENUM(…)
#define UDELEGATE(…)