why is it much easier for group 14 elements to become stable by sharing instead of transferring electrons9

Because they are closer to the farther end of the periodic table. Since they are closer to the farther end they don't want to give away their electrons because it would be easier for them to just steal them from other atoms.

Because of their intermediate electronegativity

Explanation:

First of all, any element of the periodic table interacts with other atoms to complete the octet in its last atomic level and achive stability, either losing or gaining electrons.

Group 14 elements have 4 electrons in the last level, so it would seem that for they its the same to lose or gain electrons. But actually its neither, for them is easier to share the electrons with other atoms.

This is because they don't have a very high electronegativity (making them able to steal electrons) nor a very low electronegtivity (making them anle to release electrons).

This intermediate electronegativity is the responsable of the sharing of electrons.