It's not just selling popcorn, it's about supporting and promoting Scouting.
Here's the presentation from the Popcorn Kickoff on September 15, 2019:
Pack 335 Popcorn Kickoff Presentation - Sep 2019
Scouts who sell popcorn gain confidence, learn salesmanship and communication skills, and get a sense of accomplishment.
Here are a couple of great videos with popcorn selling tips: