I hate to burst your bubble, but M&A is about as far from rational as you can get. Acquisitions are about much more than the present value of future cash flows.
As pjc50 said, it's often definitely a case of empire building.
Other times, the kind of personality that propels one into upper management makes him/her a particularly poor choice to execute an acquisition. Consider strong competitive instincts. While that is an excellent trait in certain types of companies, it can be a nightmare when it comes to acquisitions. Hell, highly competitive people can and have raised the valuation of a company several magnitudes beyond reasonable, simply through a bidding process.
In many ways, a competitive acquisition process looks like an auction and all the usual caveats apply.
failed experiments. in this case, someone at Google thought Boston Dynamics would be a good fit and that they'd be able to profitably cooperate. well, unanticipated complications prevented it. but they tried something different. sometimes these things do work out well. not this time.
