The answers range from dozens to billions, so each slider step multiplies the value instead of adding to it. You can also type an exact number.
On a logarithmic slider the same distance always means the same factor, which matches how scoring works.
Every question uses the same scale, from 1 to 100 billion, so the ends of the slider never hint at the answer. It also starts at an unrelated position, so you have to make a guess.
See also How is Closest Guess scored. For tips, read the Closest Guess tips and strategy.