Or maybe we don't feel we can demand something that has to be given freely.
Who said anything about demanding? Demanding doesn't work. Just as giving and giving and giving and telling yourself you expect nothing back doesn't work. Why? Because THAT is exactly what you will get back.. nothing... This is what doormats do.
People that have high self esteem don't keep on trying to win a man or woman by thinking the "unconditional" love option will work. It doesn't. It is just another way you hope will win their love. Giving is fine in a mutually loving relationship.
Two examples are Mr Bond and Officer. One has been doing all the giving for a couple of years. The other for a few months. Same result. Neither wife is giving much back. The proof is in the reality.