It's because it's not a race track. Race tracks are designed with safety in mind. Large areas on the outside of curves, gravel runouts, and padding on all fences.
The TT is a street track with rock walls, telephone poles and stop signs. Those things don't exist on race tracks for a reason. You're going to have a bad time hitting a rock wall at 180 mph.
You may be familiar if not, search 'Isle of Man onboard' on YouTube and you'll have your answer.
I should film the palms of my hands while watching those videos, they start glistening with sweat within a minute or two. If you've seen those insane rally car videos, these are worse. Relative to modern racing events, it's like working on the Golden Gate Bridge before they put the net up.
The TT is a street track with rock walls, telephone poles and stop signs. Those things don't exist on race tracks for a reason. You're going to have a bad time hitting a rock wall at 180 mph.