Free webhosting companies expect customers to upgrade

While there are large number of companies offering free webhosting, most of these companies are offering free webhosting only as a promotion to attract customers. There is a lot of competition for advertising webhosting online, and CPC rates for webhosting advertising on google adwords are among the highest of all categories, as it is an auction.
Since internet users are always looking for free stuff, it is far easier to advertise a free or zero cost webhosting company, as there are a large number of websites which will list free offers at no cost.
It is usually easier to convert an existing customer, rather than find a completely new customer
Usually after a few months, the free webhosting customer is expected to upgrade, especially if the website is getting a lot of visitors.