Google started publishing for several reasons but the primary one was recruitment (showing off was a secondary goal). The mapreduce, GFS, and bigtable papers played an important role in attracting an early generation of distributed computing/high performance computing people from around the valley and CMU/MIT, who helped build the second really successful versions of the web search engine (retrieval and ranking), ads serving (the auction, the logs joining pipeline), etc.

The other reason is that the leaders at Google at the time believed that we would achieve the singularity faster if Jeff Dean periodically sent ideas back 10 years in time to Doug Cutting.