Halloween was not made with Canada in mind. Sending roving bands of children into the streets of the city might work best in a place where it isn't dark almost immediately by the time school lets out. This is probably why the first Pumpkin Walk was a hit, and the area around Jaycee Beach quickly filled with costume-clad children on Friday evening. It's also why I'm going to spend the next several paragraphs praising the event, which I think managed to do the incredibly difficult task of being an arguably superior alternative to traditional trick or treating.
The reason why traditional trick or treating works is partially the sense of adventure. Even if you know most of your neighbors, there are still places you generally don't go and people you don't regularly meet. It's not so much that those places are scary or intimidating, they're just not well known, and there's really no reason for you to be bothered by this fact for the majority of the year. But for kids on Halloween, there's incentive to go to those places where they don't normally get to visit, and explore new and exciting corners of town, because there's always the promise of candy hidden in those corners. It's the only time of year when kids are really encouraged to explore, to get out and meet the neighbors and hustle them for Twix bars.
The problem with a lot of alternatives to trick or treating is that it doesn't embrace the exploration part of the formula. The majority of buildings that could host an event are certainly safer, and warmer, than roaming the streets, but they're also not buildings that are really unknown. Pile on the decorations all you want, but most public spaces are going to places that are familiar to kids and a bit less exciting to wander around on the hunt for delicious candies. This is not to disparage anyone who attempts an indoor Halloween event, but just recognition of how difficult it actually is to host one in a satisfying way. It's difficult to maintain mystery in a well lit building.
The strength of the Pumpkin Walk is that it removed the things that are actually unsafe - cars that can't see children in dark costumes - while keeping the mystery alive. It's too simple to say that just putting it in the dark was what made the difference, though it was certainly very dark. In a regular park it still wouldn't have been a very effective replacement. Instead, by building it around paths in what amounted to the woods was what made the difference. It's an event built around exploring an area, and it's even better than the regular neighborhood because it's quite rare to actually explore that part of the city at night. It worked because it understood that part of the joy of going to places you normally can't, and being surprised by what you find there.
Plenty of parents don't want to send kids out on a traditional quest for candy, they view it as a bit of a risk, especially as they hear stories about people who have ill designs on kids. This is why so many people hunger for a way to get their kids doing something on the spookiest night of the year without it being something that makes them too worried. That's likely why Jaycee Beach was packed on Friday night, but it's also an event that worked because it was still able to capture fun of the experience of trolling for candy, without the drawbacks.