Because most of the time you won’t get any.
People are in it for themselves, especially when there’s something to gain or to lose.
The only exception is with family. That is, if you’re lucky enough.
The approach should therefore be to make others want to be kind and generous towards you.
Call it reciprocity or the Ben Franklin effect, whatever it is or however you do it doesn’t matter – making it happen is what does.
Just keep in mind that some things work with some, and other things work with others. Figure those things out as quickly as you can.
Then let the kindness and generosity of people surprise and delight you, taking no credit for what you might have elicited in them.