The common law is created by human judges, and that they decide those cases according to the legal values they hold.
“Formal” judges decide cases the way earlier judges decided them, just because those judges decided them that way. These judges value stability and certainty in the law. They don’t care whether the law is right or good; they want it to be predictable. The most formal of these judges think of law as a system of narrow and consistent rules from which they construct rules they hope can be mechanically applied by the judges ruling after them.