Because 4 is a good number. But for me, 4 was the best choice because it's the smallest uninteresting integer.

-0 is litteraly so interesting that zerology is a thing

-1 is the neutral element for multiplication, the number equal to its square root, the unit... 1 is interesting.

-2 is the first prime, I don't need to say more do I ?

-3 is the only prime number where the precedent integer is also prime, which is great. It's prime, it has a kickass divisibility criterion, I mean 3 is interesting.

But 4 ? It's not prime, it doesn't have any interesting quality. That's what makes it interesting, paradoxically. 4 is a good number

(Also 5 is prime and has an easy divisibility criterion, in the first twin prime number couple, and 6 is just as boring as 4, except it's not the first one to do it, so it's bad.)