For good stability.
Your benefits:

• The support slides onto the "big foot" via the long-hole guide
• The "big foot" does not have to be pushed on the ground, as with many other commercial systems, and the support can be operated with less force
• Low space requirement during driving due to positive, spring-supported contact with the support (sufficient ground clearance)
• Super stability! Large footprint (200 x 180 mm) with chain lines
• "big foot" incl. assembly parts and instructions