I'll take a run at why a promoting amateur radio is important.
1. Hams develop highly technical skills while interacting socially.
2. With entry low cost and no subscription fees, hams have global communication abilities without cellular, internet, and power grids.
3. Hams support community, often with important emergency comms roles during disasters, war, or search and rescue efforts.
Why parks? They're easily accessed. They're free. They're visible to newcomers who wouldn't otherwise know amateur radio could be fun and social.