That's because manufacturers need marketing material. They want their product to stand out. So they find creative ways to make them look better.
Let's examine some common specifications you'll see. And then I'll tell you why you can ignore them. It will make your buying decision easier.
Contrast ratio is a popular specification, and it is important. It's the difference between a display's blackest black and brightest white. A higher ratio translates to a clearer and crisper image.
The contrast ratio is presented as a number like 1000:1. The best contrast ratio is between 1,500:1 and 2,000:1. Anything higher is most likely overinflated.
Unfortunately, contrast ratio numbers can't be trusted. That's because there is no single standardized test. Manufacturers are free to test however they like.