Here in the UK, F1 is on the BBC and Sky, so I would say its by far and a way the most known Motorsport where I live. I could ask people f they know of F1, and they would, albeit, pretty much nothing about it (and the occasional person would know Vettel). Other than that, no others get major coverage. MotoGP is shown sometimes live on the BBC, and the BTCC is on ITV all day - but neither are majorly watched. Eurosport does fairly well, with the majority of the lower league Formulas and Endurance Races being shown on it, and Motors TV do quite well too, but once again, none of these are mainstream broadcasters and are not very well known to those who don't watch motorsports.
Its not that they don't get coverage, its just that they're on the wrong channels which doesn't help the matter. If Le Mans, for example, was on the BBC, I'd assume a lot more people would pay attention to it, solely for the larger audience the BBC has. But once again, the sheer cost of following a Motorsports season or even race, appears to cost more than your standard Football or Rugby match.