I think it woks, just not really by itself.

It's basically like any other form of marketing. It's probably not going to be the sole reason why people buy it, but it will shine a spotlight on it and the people running it hope that some people find the game interesting enough to buy it

It does also just straight up work with a lot of kids. My niece and nephew got Smash Bros and now they predictably want to try other games that their favourite Smash Bros characters are from.