Why is the structure of H2S2O5 unsymmetrical and not symmetrical..?Also if there is a S-S linkage then why is there no term like `THIO` included in its name?

I understand that. But why don’t we consider the symmetrical structure?

Because in the Maharashtra HSC board textbook it is given as symmetrical sturcture(the one with +4 on both sulpurs with a S-O-S linkage.) This even justifies its name i.e. “PYRO”