Fry: Hey, professor. What are you teaching this semester?
Prof. Farnsworth: Same thing I teach every semester: The Mathematics of Quantum Neutrino Fields. I made up the title so that no student would dare take it.
First reason is that quadrilaterals can be mapped to a square and so you can use "Tensor product" elements which is just a fancy way of saying that you can uncouple the equations to be 1D for each direction. So you can think of your problem in 1D and easily extend them to 2D by using quadrilaterals.
Second is somewhat related and is sparsity. The matrices generated for quadrilaterals would be sparser and hence your performance will be higher.
Third is accuracy. Quadrilaterals are regarded to be more accurate however I am not sure there are proofs or conclusive studies on this, more a rule of thumb.