Soft SUSY breaking fermion mass terms in MSSM for matter fields

Question

In the MSSM, the chiral fermion fields (the Higgsinos) don't have any soft SUSY breaking mass terms and trilinear interactions while their scalar superpartners have so, whereas naively it should have been the other way around. The gauginos too have soft SUSY breaking mass terms. 

1.  Why do the chiral fields have such a distinctive feature?

2.  In addition to this why do the scalar Higgs also have $L_{soft}$ terms?

3. Also how do we calculate the coupling parameters of the $L_{soft}$ terms starting from first principles? Or are these parameters arbitrary?