@nwatn that's explained in this chapter already
S ranks before never gave a shit about money or fame, they just were there when they were needed, same as Saitama, he always does all the work and leaves without informing anyone he did anything.
That entrance exam was a satire in of itself, that's why Saitama got the lowest rank, cuz he miserably failed the non physical test part, while Genos easily got into S rank
Also it's not necessarily physical abilities, there are those heroes like Tatsumaki with her supernatural esper powers, doutei(child emperor) who's just a genius, Atomic Samurai whose martial skills surpass understanding same as Silverfang's, but yeah, it mostly is filled with raw physical power