That would be the case even without politicians doing favors and handling out monopolies, and asking for all kinds of BS regulation that only big manufacturers/companies can afford.
After a company gets large enough (because of competence) it's not easy anymore for lesser companies to compete with it.
That might have been the case back in Adam Smith's time, when it just took some ingenuity to come up with an idea, and the money to build a few factories, which were much simpler and 1/100+ the cost of today (inflation adjusted).
[That was true even back in "early web" days. It was much cheaper to make your own competitive search engine that it is to compete with Google today].
It might also have been easy when new paradigms were taking off, and old companies couldn't work with them (e.g. switch from mainframes to PC), living a spot open. Now big companies can diversify more easily, predict future trends (like Google adopted to a mobile world, and will adapt to VR or whatever comes next).
Now the technologies are more involved (even in "non tech" companies) and the stakes higher. Even if you can just design your advanced product and order units from a generic chinese manufacturer, you wont get the same economies of scale, preferential treatment, distribution, etc, as a large company.
And if some wanabbe company gets threatening enough, a bigger company can just buy it. Especially since going to the stock market as opposed to being self-owned means all companies are up for sale.