Im not sure if this is what you're referring to but there is this trend, kinda similar to gender reveal parties and enormous weddings and stuff, for parents to have really elaborate birthday parties for their kids, and sometimes "smash cakes" are part of those parties. My cousin does them for her kid. I find it very weird. They serve one cake for all the guests and then have a smaller smash cake for the birthday kid that they kind of smash up and eat while a photographer takes smash cake photos. If you search smash cake on Instagram especially you'll see what I'm talking about.

I think it's just a marketing trend and a social media parents made it popular kinda thing.