why the bearing metal temperature are different for turbine front thrust journal bearing and for all other turbine journal bearings...

 

Most thrust bearings are not journal-type bearings. They are "Kingsbury"-type thrust bearings. (Use your preferred Internet search application to look up this and various other types of thrust bearings.)

Journal bearings can can have different temperatures because of the different loading, different dimensions (internal sizes), different positions (changes in bearing support/turbine casing with heat and age), etc.

Thrust bearings for heavy duty gas turbines usually have Active and Inactive thrust temperature indications.