Why does an electron found in a 2s orbital have a lower energy than an electron found in a 2p orbital in multielectron systems?
The energy in the 2s is less because the orbital is simpler and has less probability distances than the 2p orbital.
The 2s and 2p orbitals have the same average distance from the nucleus. This would give them the same energy level.
However the 2s orbital is a simple spherical orbital The Probability distances are found within the sphere.
While the 2p orbitals are barbell like structures with two lobes. The Probability distances for the electrons to possibly be in the outmost parts of the lobes is require greater energy than that required to be found inside the sphere.