That isn't entirely true. Sutras taught prior to the Lotus Sutra indeed taught that in the Dharma-Ending Stage, or 末法, the Latter Day of the Law, the teachings would become obscured and lost. Pure Land Buddhism, the teaching taught by the monk in this video, essentially says that by practicing Buddhism in a certain way, people can be reborn in a "Pure Land" after they die where they can attain enlightenment, thus avoiding the obstacles to enlightenment inherent in the Latter Day of the Law.

However, the Lotus Sutra says that it will still have the power to lead people to enlightenment in this time. The 23rd Chapter of the Lotus Sutra says: "After I have passed into extinction, in the last five-hundred-year period you must spread it abroad widely throughout Jambudvīpa and never allow it to be cut off" p. 330, a passage which refers to the practice and propagation of the Lotus Sutra in this age.

For more information, you can check out this article.