AS11-40-5878 (20 July 1969) This iconic photo is not of Neil Armstrong's very first step on the moon. It's not even his footprint. It was made by Edwin E. "Buzz" Aldrin Jr.
This photo wasn't taken for future posters, T-shirts, mouse pads etc., but for a strictly scientific purpose: to study how the moon soil (regolith) would behave when compressed by the boot, and thus learn something about it's geological properties. That's why Aldrin also took a photo of the surface before he made the footprint.
One important objective of the Apollo 11 mission was to observe the properties of the regolith and assess how these properties affected the crew's ability to move about and to work on the lunar surface. This investigation was known as the Soil Mechanics Investigation, which on Apollo 11 consisted of verbal descriptions by the crew and close-up photographs of the regolith, including three-dimensional stereo photographs.