Cupcake, why are you o obsessed with why?!
Why have 1, or 2? Do you need reasons for 2?
If it helps, I have 4, and always wanted 4. And I can answer why too, though I'm sure everyone has thi own reasons.
I have 1 sister, close in age, never got on. She was always very dominant. V intense and. Painful relationship. So I never wanted just one, didn't like thought f only child, didn't want 2 s too intense, 3 seemed more likely one would be left out - 2's company & all that, so for me 4 was always the magic number, and am luckily happy it seems to have worked out. So far
Mine are 17 months, 3 years and 5 years apart. Wanted 2x1.5 year gaps, but number 4 took lterally years to come along. Had given up tbh.