Why is cis-trans isomerism not possible in coordination complexes with tetrahedral geometry?

Tetrahedral complexes do not show geometrical isomerism because the geometery of the ligands is definite as any two ligands lie at 109^o28’ . Therefore the relative positions of  ligands are same with respect to each other.

Thus this mean they the bonds of same groups can neither be at the nearest position(cis isomer) nor be at the farthest position(trans isomer)?

In tetrahedal geometry no mater if you change the position of ligands from nearest to farthest on paper but both are actually the same if you imagine a 3D shape and look from other side .

All ligands are adjacent to each other at equal angles , so when you change the position of a ligand it will be same again . Try to imagine in 3D.