Because its our most potent weapon against her. To the degree you allow her to distract you from chanting well, you become malleable to her will.
Chanting is the waxing moon that spreads the white lotus of good fortune for all living entities.
Sri Chaitanya Caritamrta, Antya 20.12,
Chanting Hare Krishna increases the ocean of transcendental bliss.
In order to be recognized by Krishna, the Supreme Personality of Godhead, one should chant the holy name of the Lord continuously, twenty-four hours a day.
Srimad Bhagavatam 4.23.7
The Perfect spiritual practice for this age is to chant holy name with full conviction and to make others also chant the holy name of the Lord.