Hi! a "big draw" means a big source of attraction. If something is a big draw, it draws people's attention to it/attracts a lot of attention

When a lot of people come to see a show we say the show "draws a crowd." We can also say the the show "attracts a crowd." Something that is very effective at drawing a crowd is "a big draw." Here are some examples of use. "We visited Yellowstone National Park last year. We saw a group of cars parked at the side of the road so we pulled off, too. There was a mother bear and cub on the hill nearby. Wildlife always draws a crowd." "The big draw at Yellowstone National Park is Old Faithful, a geyser that erupts every sixty to ninety minutes." "Yellowstone National Park draws over three million visitors per year, from all over the world."