Being asked to tip at nova wild?

I went to nova wild the other day, got two tickets and a tub of feed for the animals. Was quite pricey but It’s fine, after paying I was given the tip screen, which had a minimum of a 15% tip of $8.50. I of course said no tip, but after selecting no tip I noticed the lady behind the counter go from being overly friendly to dropping the act and seemed a bit annoyed. I’d love to know what the tip is going toward? I could absolutely understand a donation towards the animals or even a tip for the keepers, but who is this tip actually going to? I found it bizarre. I’m not from America originally so unsure if this is normal and I’m over reacting. Just feels like I can’t leave the house without a hundred people with their hands out expecting money for nothing. As tho we’re not a struggling right now