Hayss from my understanding, nobility didn't start just because they wanted to.
They became a nobility because they are part of the founder of a nation, contributed greatly to the nation or other important reason. Thats how they started but the thing is, that achievement was passed down to their descendants resulting to being born a nobility without the actual reason aside from having a lucky bloodline. Altough you can't deny the contribution their ancestor did, it was also shitty to receive special treatment just because you were born in a noble family. So yeah its unfair system but also have a reason why it happen in the first place...