Why? Simply because you have to be full before you can give. You have to have before you can share. You have to be in your own alignment, before you can share true alignment with others. Not always, but most of the time.

Whatever that is. Alignment, freedom, support, love, space, healing, happiness, joy, financial abundance, time and basically energy.
All of these you have to give from a place of knowing what that actually is, not just because society or a spiritual guru says so.
It is literally impossible to give someone something if you don't know what that is yourself, if you don't embody it within you. It's simple. It's law.
And if I look back into my life now, how much I gave without having. How much I "loved" without loving myself, how much I wanted to help, without helping myself. It was never sustainable. It was somehow conditioned.
I literally "gave" to the point that I ended up being homeless, broke and broken. No matter how naively carring, protecting, humble and selfless I wanted to be. And this was my pattern for a while. Then I hated myself for it. I created a very unhealthy give-receive dynamic within me. I needed to learn the hard way.
Our needs and desires should always come first, period. This way, maybe we don't become a society of addicts anymore, depending on one another for energy. Maybe the word sacrifice wouldn't be necessary to use anymore.
Maybe this way we are courageous enough to look within ourselves and find that connection with Source which screams to be acknowledged and explored. When we give from there, it is a life-changer, it is cooperation, it is expansion and honoring.
We have this weird conditioning to be nice, to give all the time no matter what, to just show up for one another to the point of our own well-being and well-functioning. Be honest, does this every work for you?