Here's why:

* Enzymes are catalysts: They speed up chemical reactions but are not consumed in the process.

* Substrates bind to enzymes: The substrates are the molecules that the enzyme acts upon.

* Enzymes facilitate the conversion of substrates into products: The enzyme helps the substrate molecules interact and form new products.

Think of it like this:

* Enzyme: The baker who helps combine ingredients.

* Substrate: The ingredients (flour, sugar, etc.)

* Product: The finished cake.

The baker (enzyme) doesn't become part of the cake (product), they simply help the ingredients (substrates) combine.