The question should be: Why was quality of steel lowered? Is fincantieri only firm that designs fleet tankers? If Yes, does all navies have their fleet tankers made of commercial grade steel? If NO, Why was no other firm considered? What are the cost benefit analysis of using commercial grade steel ,instead of warship geade steel in support vessels?
Who took bribe from Fincantieri is a rhetorical question. Even if Sonia did not took the money ,the very fact that Italians are over-represented in dirty tricks department compared to their size, means that Sonia is directly or indirectly influencing decision making process.
This becomes graver in view of the fact that India ,itself (SAIL), manufactures warship grade steel which is being used in IAC-1.