Perhaps this particular case has motivations similar to the ballon project, i.e. more internet access brings more ad impressions.
Sure, self-driving cars and satellites can be used to cut the cost of making maps to sell ad impressions against, but that's like buying an oil refinery as a fuel hedging strategy[1]. Plus unlike many of the web properties Google buy, Titan could probably turn a profit even operated entirely independently, and diversification helps. On the other side of the equation, Lockheed Martin has been buying up software companies focused on the logistics of running passenger airports.
[1]Delta Airlines actually did this...