'Ointment' in the Bible

And it was that Mary who anointed the Lord with ointment, and wiped his feet with her hair, whose brother Lazarus was sick.

Mary therefore took a pound of ointment of pure nard, very precious, and anointed the feet of Jesus, and wiped his feet with her hair: and the house was filled with the odor of the ointment.

Why was not this ointment sold for three hundred shillings, and given to the poor?