Molds grow better on some kinds of breads than others depending on the ingredients used and how the bread was made.
Some breads are dry and some are moist.
Some breads are even acidic, such as sourdough. Some may have fruit or nuts or other ingredients added. Many commercial breads are made with preservatives that hinder the growth of molds and bacteria to prevent or delay spoilage. Bread baked fresh in a bakery that doesn't use preservatives will more likely become moldy faster. All of these factors can influence how much mold will grow on a particular kind of bread.