Why are enzymes proteins?

Proteins (also known as polypeptides) are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues.
Different proteins have different cellular functions, for example, a group of proteins form the cytoskeleton which allows the cell to maintain its shape and size. We call them structural protein. Another group of proteins catalyze chemical reactions, they are enzymes.
Almost all enzymes are proteins, that means they are made of amino acids.