that’s a plain and simple answer… a lightsaber’s blade is composed of ENERGY that is channeled through a crystal inside the saber’s construct. Energy makes the saber super-really hot, making it able to cut through solid objects
now, when 2 lightsabers’s blade collide, energy can’t cut through energy, and since crystal’s vibrations are alike, the energy can a) merge or b) repulse eachother… and since both energy fluxes moves in opposites directions that’s why they collide instead merge eachother…
please, before making a meme, get your facts straight. Thanks