I am pretty sure that: (1) they have different teams working, building this didn't slow anything else down; and (2) this was built as a test project for some facial recognition technology that we will eventually see in more useful products, and needed to be tested anyway.
You're probably failing to see the real purpose behind these kinds of web pages created by Microsoft (remember the "how old am I" and the one looking for twins/similar looking people?)
These pages aren't just for fun, they're real research projects created by Microsoft in order to improve the accuracy of facial and image recognition algorithms. It's data from these experiments that makes Windows Hello/Hololens/whatever as good as it is/will be.
Making something fun and engaging helps the research to reach more people in a more fun way.