

Thing about Nessy is that it is localized. It started in an area in Scotland. Assuming Nessy was a worldwide phenomenon where sightings are found more than a couple of times a month, it’d be different.
Nessy is purported to be a single creature living in a single Loch in Scotland; why would there be sightings elsewhere in the world? That’s like saying “The Eiffel Tower is only ever sighted in Paris, isn’t that suspicious?”
Given the relatively small number of visitors to Loch Ness vs. the number of people in the world with cameras who could presumably document aliens or ghosts, I’d argue that the sightings per visitor are at a significantly higher rate than UFO or ghost sightings.
Depends on the puzzle; it’s certainly possible to design Sudoku puzzles that necessitate guessing, but most do not. It’s possible you’re just not familiar with some of the more complex ways to make deductions.
Maybe check this list - it could be that your puzzle requires some of the more advanced techniques that you aren’t using.