What is the reason for the rise of portrait photography?

1839, photography officially came out. At that time, the exposure speed of film was slow, and it sometimes took dozens of minutes to take a portrait photo. Therefore, portrait photography started slightly later than still life, architecture and landscape photography. Nevertheless, photography is better than painting in realistic performance and its cost is lower than painting. As a result, portrait photography gradually replaced portrait painting and became a new industry. In the 1940s of 19, portrait studios of all sizes appeared like mushrooms after rain in major cities in Europe and America.