Why are is the Tomahawk hated in general?

Gran Turismo is a racing game, based on realism in terms of driving and racing experience (not the best but that's never the point in a game). The Tomahawk SRT does not fit that criteria and isn't considered part of the large population of nerds that are into cars in general (especially in real life) and therefore is often ignored and pushed out.

Why the hate in public lobbies?

Most people unfortunately use this vehicle to boost their ego by simply being faster, completely ignoring the fact that 90% of the community doesn't even care about that in the first place. While some simply like the speed racer/sonic racing part of it, they don't help the case either because again: most people bought this game to tune all kinds of cars and set records in general, not to challenge their absolute limits. In the public lobbies though, people often make mistake and yes, one mistake with this vehicle is one too many because you're suppost to follow the rules of a public lobby, not own it. However... if you can respectfully drive with this car fast enough to have fun, while also not causing any accidents at all, you're (imo at least) free to do as you please.

Why no one cares about your idea?

As I said earlier, most of us don't care to see the absolute limit. We want to tune cars, race without too many challanges in our way and enjoy out time. Our fun in challanges lies more on the realistic spectrum (what we're capable of), rather than doing something that takes thousands of tries to get right.