The element of earth can only come together when all the other elements have been brought together to be manifest in the physical realm. This is the beauty of Earth. Air and Water and Fire (sun, energy, light, etc.) come together to create growth and life.
In numerology, 10 would always reduce to 1, but in the Tarot, 10 has it’s own meaning and correlation, and thus while it can be reduced, it isn’t. Thus, there is a special link between the two numbers, in that both resent and end and a beginning.