ArcGIS 10.3.1 has no transformation for GCS_Clarke_1880 to GCS_WGS_1984. Why is this the case, what have I missed?  Do we have to write a custom transformation? There a heap of Clarke transformation equations on stack. But I don't understand why.

GCS_Clarke_1880 WKID: 4034 Authority: EPSG

Angular Unit: Degree (0.0174532925199433) Prime Meridian: Greenwich (0.0) Datum: D_Clarke_1880 Spheroid: Clarke_1880 Semimajor Axis: 6378249.144808011 Semiminor Axis: 6356514.966204133 Inverse Flattening: 293.4663076556253

To

GCS_WGS_1984 WKID: 4326 Authority: EPSG

Angular Unit: Degree (0.0174532925199433) Prime Meridian: Greenwich (0.0) Datum: D_WGS_1984 Spheroid: WGS_1984 Semimajor Axis: 6378137.0 Semiminor Axis: 6356752.314245179 Inverse Flattening: 298.257223563

ArcGIS 10.3.1 has no transformation for GCS_Clarke_1880 to GCS_WGS_1984. Why is this the case, what have I missed? 

Do we have to write a custom transformation? 

There are a heap of Clarke transformation equations on stack. But I don't understand why.

GCS_Clarke_1880 WKID: 4034 Authority: EPSG

Angular Unit: Degree (0.0174532925199433) Prime Meridian: Greenwich (0.0) Datum: D_Clarke_1880 Spheroid: Clarke_1880 Semimajor Axis: 6378249.144808011 Semiminor Axis: 6356514.966204133 Inverse Flattening: 293.4663076556253

To

GCS_WGS_1984 WKID: 4326 Authority: EPSG

Angular Unit: Degree (0.0174532925199433) Prime Meridian: Greenwich (0.0) Datum: D_WGS_1984 Spheroid: WGS_1984 Semimajor Axis: 6378137.0 Semiminor Axis: 6356752.314245179 Inverse Flattening: 298.257223563