The main point is why? 'not specific to neutrino' there is where the issue is. Neutrino is unique on itself therefore the ' why?' should not be tagged to the others.
They is the question of mass and quark generations.the 'why?' should help us understand that.
Anyway (further clarification) from the PDF diagram the arrows direction tells us alot,reverse every arrow and u end-up getting anti Neutrino..in the same diagram there is 'primordial Higgs field' our(Neutrino) small masses,the issue of flavour,in the diagram if we pair the arrows and oscillate within the pairs we end up with three flavors.
Then the same problem 'why?' arises, that is, the direction of arrows.And leads us to another issue 'where from?' let us digest that.
My take,Neutrino is more 'fundamental' than the other flavored particles i.e it intiates formation of flavors and mass in other elementary particles (or it's at that initial point where those properties emerge from).
About being a 'ghost and a wanderer' in the universe..hhhh it's a moderator..it smoothen Spacetime fabric by picking quantum fluctuactions here and throwing them there therefore helps in distributing energy density in the universe as it expand.
Hope The moderator won't throw me away(it's a joke)