Google is a big place. There can be multiple people working on similar ideas (see Chrome OS and Android). If the projects are small it would be common for them

Google is a big place. There can be multiple people working on similar ideas (see Chrome OS and Android). If the projects are small it would be common for them to not even know about each other, at least for a little while. If you tried to enforce that everyone who wanted to work on similar things had to work together you would burn a lot of energy arguing about "similar" and relatively minor differences in direction. Sometimes it is easier and better to just let there be separate efforts and the market (both the internal attention market, and in extreme cases, the external actual market) can decide.