Why do planes always land on rear wheels instead of the nose wheels?
Aircraft land on the main wheels. For aircraft with nose wheel it is the back ones, but for aircraft with tail wheel (also called “tail-draggers”) it is the front ones. In either case the main wheels are very close to centre of gravity and carry most of the aircraft's weight, the nose or tail wheel only carries a small fraction of it.

The aircraft must land on wheels that are close to the centre of gravity (longitudinally). If they were not, the force on the wheels would create a moment that would violently pitch the aircraft. Actually, tail-draggers tend to bounce on landing a bit because there still is some moment left and in case of tail-draggers it pitches the aircraft up.

Early planes were almost all tail-draggers, because that layout is more robust, handles unpaved runways better and has less drag when the gear is fixed. It however provides poor directional control especially once the tail lifts off the ground during take-off roll. Later most designs started to use nose-wheel, because it provides better directional control, is directionally stable, makes the floor level when the aircraft is standing so loading is easier and visibility during taxi is much better and with invention of retractable landing gear the drag didn't matter any more.