Some combination of excitement and fame seeking. Finding a new pig isn't particularly impressive, finding a new human ancestor is universally more impressive, with the added bonus of making the USA relevant to human evolutionary history.
I've never seen any indication that Nebraska man was a deliberate fake, merely an enthusiastic error.
As to how did it get a scientific name? They aren't awarded by the ultra board of science... anyone can name something, but it's unlikely others with recognise it. This sort of thing can take a while as different scientists review and publish research and justifications.
The media can get involved as well to give a misleading interpretation of evidence and events.
An interesting modern example is the Denisova fossils... we have no skull, but there has been genetic studies done. Scientists haven't given it a scientific species name because they don't know for sure if it's a variation of modern humans, Neanderthals or an example of the Homo longi species.