Well of course a government that attempts to do all that will be very powerful. And, of course people will spend large amounts of resources to influence a government with that level of power.
Once they have gained control over an industry, let's say steelworking or railroads, they become like feudal lords in that industry, setting wages and prices however they wish.
Power is subject to a positive feedback loop, whether it's political power or economic power. Having power makes it easier to gain more power. That's why it will always tend to concentrate in the hands of the few.
Government power in a democracy comes from a game of "artificial equality": elections in which every person has one vote, regardless of their power "in real life". (This is different from the economy, where your power is proportional to your wealth.) For this reason, it can act against the natural tendency towards concentration of power.
They're all in it for themselves. The key is to ensure that there isn't a big enough state to corrupt so they can consolidate and entrench their power.
A small state prevents monoloploies from being formed and from using those wielding power to consolidate their power. And then it doesn't matter how evil the guy who gets the top job is, because he just can't make a big difference.
At the heart of all this is how England managed to keep its Anglo-Saxon self-government traditions even after the continental Norman invasion and takeover. Because the Normans could only ever wield limited power at the state level, they could never fundamentally change the way the content was run at a local level. So citizen assemblies and English common law continued and was never replaced with continental law, the final iteration of which is based on napoleanic code. Thus in England, and her spun-off colonies, you're fundamentally free to do your own thing unless there is a specific law against it, while most other places state that you can only do something if there law explicitly states it.
This fantastic inheritance was all bequeathed to the citizens of those countries with legal systems based on common law precisely because England had a weak central government which reduced the ability of a king to control everyone, especially when that was a foreign king who had invaded.