The famous close-up photograph of the Apollo 11 bootprint was captured on July 20, 1969, by lunar module pilot Buzz Aldrin.
It was taken for scientific purposes. Aldrin deliberately stepped into the pristine lunar dust and photographed the indentation to help NASA scientists analyze the soil mechanics of the lunar surface. By studying how the fine grains compressed under the weight of an astronaut, engineers gained crucial insights into the load-bearing capacity and texture of the lunar regolith.
Because the Moon has no atmosphere, there is no weather, wind, or rain to erode, soften, or sweep the soil away.
Actually, the only natural threat to these historical markers is the incredibly slow bombardment of cosmic micro-meteorites.