The concept of hybridisation is completely derived from experiments. you note the angle of a molecule, you try to define it from theoretically. that is why a particular hybridisation cant be justified. on basis of vsepr, attraction and repulsion, molecules and shapes can be justified (position of lone pairs, in specific)
but, there is an explaination. we say, hybridisation lowers down the energy. what do we mean by that? in this case, if bond with p orbital is made, then, it will be weaker because p are located far from nucleus. Have you ever noticed that every hybridisation requires a s orbital? inclusion of s orbital is a necessity for every single bond, closer the electron cloud to the nucleus, more will be attraction. hence, stability will increase.
more s character leads to more electronegativity, why? as s character increases, electron cloud becomes nearer to the nucleus, hence strong attractive forces are in action.