Years ago in the Economist I read about a study that has stuck with me since. According to a study of public company mergers, "Only a disappointing 17% of mergers had added value to the combined company, 30% produced no discernible difference and as many as 53% actually destroyed shareholder value." [1]
That certainly matches my impression. My subjective opinion through friends is that acquiring companies rarely fully understand what they've bought, and pretty regularly kill what makes the acquired company special. Not on purpose, really. I imagine an enthusiastic cartoon monster running around trying to hug people it takes a fancy to. Some it squishes to jelly, some merely end up bruised, and some it neglects or drops when its whims turn elsewhere.