Because mindfulness requires a commitment to regular practice. If there is no commitment, then the mind can easily be drawn back into it’s old ways. Modern life holds so many distractions and it bombards us with so much information that it can lead the mind astray easily.
Jon Kabat-Zinn, who pioneered secular mindfulness says the following:
“Making a time for formal practice every day is like feeding yourself every day. It is that important.”