The best reasons for M&A (merger and acquisition) are when two organizations possess complementary resources that combine to deliver customer satisfaction more efficiently and/or effectively.
This can range from economies of scale, to synergies of talent, and (strategically) can be a viable competitive tactic during the “industry-shakeout” stage (early maturity) of an industry life cycle.
Motives can include the will to utilize capital, improve management, combine knowledge, but also to develop barriers to entry for market challengers and followers.