> why is that

Why buy 1mg pill when you can buy 100mg pill?

Even funnier is that often 0.25mg or 0.5mg is closer to the correct dose, and those sizes tend to be hard to find.

There actually is a condition that calls for extremely high (100mg+ doses), but it is a very rare thing, no one should ever consider that much without instruction from a doctor. But you'll find it right next to the normal <=5mg doses without any explanation.