Why are you surprised?
There are a couple fundamental issues with capitalism that are failing to be addressed here: monopolies, and natural monopolies.
Capitalism really is less about competition and more about accumulation of capital. The competitive behavior is the goal, but it comes with the built-in problem of monopolies. You can't allow people to 'win' this particular game. Taken to an extreme, you might end up with one company that simply owned everything.
Capitalism in this sense is kind of a bait-and-switch. We're sold on the idea of an efficient competitive marketplace, but end up with monopolies and rent-seeking.
The problem of natural monopolies is even worse. Your ability to start a competing business is almost entirely a function of how much initial capital it takes to enter said market. It's far easier to start a restaurant or web company than to start a company that lays undersea fiber optic cable. This is why people talk about 'barriers to entry' as a bad thing: they reduce the efficiency of the market. Further, there are some services where competition would have negative utility -- no one really needs multiple companies laying water, power, or sewage lines to their home.
The answer to both of these problems is government. The government's purpose is to prevent or eliminate these market failures.
With natural monopolies, there is no real purpose behind allowing them to make a profit. It's a form of taxation, and can justly be called a theft from the public. These markets are the natural purview of government.
We have a slightly larger toolbox for dealing with large companies. We can break them up entirely, levy progressive business taxes, or subsidize potential competitors.
We need to start divorcing the idea of competition from the idea of capitalism: they're not synonymous. Yes, I am anti-capitalist -- but very pro-competition. Which side are you on?