You have potentially very serious problems if the company runs into trouble, or simply changes direction, though. If a local authority runs into financial trouble, then depending on the jurisdiction, it may be given more money by the central government, or bailed out, or given artificially cheap loans, or similar, but it will rarely just be _abandoned_.
With a company-run town, however, you have a serious problem. What happens when things go wrong? One solution, of course, is that the local authority takes over, and this has happened a lot in many countries on a smaller scale, with privately managed housing estates and so on taken on by the local authority, but this really isn't a great solution; it's expensive for the local authority and an essential subsidy to the company, and couldn't be permitted on a very large scale.
In particular, you'd expect a company run town to be a disaster waiting to happen in the case where a property bubble collapses.
Of course, there are other problems; unless you're very careful, and regulate heavily, you'll end up with uncompetitive local supermarkets, and so on, for instance. And at a certain level of regulation, you're just using a private company to perform a government function, with the government telling it how to do it; this is almost never cost-effective.
Detroit today rather acts as a proof against what you're claiming. And that involved a lot more people than a small corporate town ever could. In fact it was arguably the most important industrial city of the 20th century.
They've allowed Detroit to just gradually erase from existence. It is being abandoned. They're demolishing parts of it that are decaying. In many parts of Detroit they can't pay police or teachers; they can't support fire fighters or other basic services.
With a company-run town, however, you have a serious problem. What happens when things go wrong? One solution, of course, is that the local authority takes over, and this has happened a lot in many countries on a smaller scale, with privately managed housing estates and so on taken on by the local authority, but this really isn't a great solution; it's expensive for the local authority and an essential subsidy to the company, and couldn't be permitted on a very large scale.
In particular, you'd expect a company run town to be a disaster waiting to happen in the case where a property bubble collapses.
Of course, there are other problems; unless you're very careful, and regulate heavily, you'll end up with uncompetitive local supermarkets, and so on, for instance. And at a certain level of regulation, you're just using a private company to perform a government function, with the government telling it how to do it; this is almost never cost-effective.