The real cause of Greater bond angle is that the repulsion between the lone pair of electrons or between thebond pair of electrons.

When  in a compound Carbon is sp³ hybridised then there is formation of 4 single covalent bonds which are sigma bonds, the 4 H atoms arrange tetrahedrally so as to minimise the force of repulsion between them  so the angle is 109.5⁰ But  in a compound Carbon is sp² hybridised then the bond angle increases to 120^o  because of repulsion between the bond pair electrons.But  in a compound Carbon is sp hybridised then the bond angle increases to180^o  so as to minimise the force of repulsion