Why is there so much virtual environments?

I'm new here and excited to see your wonderful introduce of operating system. But I've found that there have been much virtual :

1. vagrant with virtual box(32-bit) .
2. qemu which is 32-bit

Is it necessary to do so? If the 1 step is to build a 32-bit env, why don't we just do it use qemu ?

Thanks in advance.