The amount of cholesterol in the blood is largely produced by our own body depending on the mix of fat and carbs that we eat, and a smaller but still significative part comes from dietary cholesterol.

Most people eat more than just an egg a day in terms of cholesterol. They eat dairy, meat, eggs, and fish multiple times a day typically one or more of those at every single meal.

So dietary cholesterol does add up over the day, combined with a bad mix of processed carbs and fats it's a recipe for disaster.

Yes, you can eat one egg day and get away with it, but most people eat way more cholesterol than that every single day.