Why is Yukihira Soma not famous at Tōtsuki Culinary Academy? It is a known fact that Yukihira Soma is the son of one of the world's most famous chefs, Yukihira Joichiro, but why is it that the students from Tōtsuki Culinary Academy don't know about Soma?

It's even stranger that Nakiri, who is known as the God's Tongue for her extreme tasting skills, admires Joichiro but fails to realize that Yukihira Soma is the son of Yukihira Joichiro. She had seen Soma's application form, so it must have given her a hint already. One of the few people (or maybe the only one) who seems to know about this fact is the headmaster.

Why is that? Are they trying to hide the fact that Soma is the son of Joichiro, probably for some unknown reason?
I have not read the entire manga, but I read that Soma's father was formerly known as Saiba Jōichirō. It is not the same last name as Yukihira Soma, so this may be a reason why people don't know that they are father and son.

Source: Jōichirō Yukihira on Shokugeki no Souma wiki.