We have a mixed economy. That means the government supports the private sector in small and large ways, and, on behalf of the public interest, is entitled to a share in the profits.
I'll use a simple example. Consider how much support relay services like trains and the airline industry have received from the government. Then consider how much private sector businesses, small and large, rely on those services to move products, people, and information. Imagine how much difficult this process would be if trains and airlines folded altogether. Other businesses could buy shares in the industries for the sole purpose of keeping them open to continue moving goods, but their quarterly profits are comparatively small to the government's revenue. And lacking the ability to secure large and pay loans, they wouldn't be able to finance the burden of bail-outs as effectively.
Furthermore, no single business, no matter how large, would be able to support the airlines by themselves. So they would have to form coalitions with institutions they normally compete with. These alliances might be tempted to use their ownership to exclude businesses from moving their goods via train or airplane. That would be a short term gain for the alliance, but it would impede economic growth overall and lead recession.
So, the government supports the relay services and manipulates the law so that they function as a 'neutral ground' which, while inconsistently profitable in-themselves, drives success in other areas of the market.
A mixed market economy is the only way to produce and maintain a technological revolution where inventions like the 'Internet' are possible. One of the consequences of a mixed market economy is that is requires a big, active, high spending government.