I wouldn't say it is propaganda (that's a strong word!), but these entities, common in many people's folklore, have no basis in fact. You can ask /r/Askanthropology about things like the "giganthropus" fossil evidence, but whatever that represents, it is hardly evidence of giants, and it would be an incredulous stretch to conclude that there was some sort of primal memory of gigantic hominids many of hundreds of thousands of years ago - if they ever existed at all!

Giants are one of that species of supernatural beings that existed in a remote past: people talked about encountering ghosts, fairies, the devil, or any number of others things, but they never told of having encountered a giant. Stories about giants were always about other people living in the past having dealing with them. It seems that it was easy for people to imagine there was once a race of titans to explain enormous, seemingly unnatural things in the landscape. The name of the Giant’s Causeway preserves the idea that one of these entities built a path to walk from Ireland to Scotland. Wade’s Causeway, is another reference to a giant, in this case to explain a Roman road in Yorkshire. The etiological role of giants was paramount, but the explanation of the landscape, megaliths, or extraordinary things in general could merge with stories about other supernatural beings. For example, the Devil’s Dyke in Cambridgeshire is an example of tradition holding that Satan affected the landscape in a way normally reserved for giants. I wouldn't want to go so far as to say it was a process of 1. fantastic landscape element; 2. fantastic and necessarily large entity needs to be responsible; therefore, giants must have existed. That said, this sort of process serves as an underpinning to reinforce belief.