You can follow all the illegal monopolistic/oligopolistic activity at these sites:
Individual companies are pursuing growth opportunites thru M & A. Since corporations have almost $2 trillion in cash, we are seeing unprecedented activity. The company being acquired often has a >10% rise in their stock price.
But the marginal social costs exceed marginal social benefits!
Consolidation forces the closure of plants and mass layoffs. This ruins both consumption and tax revenues at the local level. So we don't see an increase in GDP, rather, we see an increase in corporate profits.