Lots of generalizations in the OP, though anecdotally often true.
My company has been bought and sold twice in my 13 years here, and we have bought and sold a number of businesses. Sometimes we created lots of value for our shareholder and sometimes not. On balance its been a net positive.
In our industry, consolidation to achieve economies of scale represents one of the best strategies available to counter the secular trends we face which are declining margins from our customers, and increasing costs due to technology and regulatory compliance. As an operationally leveraged business, scale and volume are how we preserve our bottom line margin and its generally not possible to grow our market share organically - thus we often look to inorganic growth strategies.
Full disclosure: I am the CFO of the company, and I did not get filthy rich off any of the M&A activities of our firm - If I did I wouldn't be working anymore
