The carbon atom is very small due to which its outermost electrons are strongly held by the nucleus. So it is not possible to remove 4 electrons nor it is possible to gain 4 electrons(atomic no-6). since carbon atoms achieve the inert gas electron arrangement only by sharing of electrons.therefore it forms covalent bonds.

The reason for forming large no compounds:-
1) the property of catenationĀ (the ability combine with other atoms)
2) due to its valency 4

hope this satisfied u....