Why is the site installed on a virtual machine?

Question

Debian

Guys, for a long time I did not do web development and is very outdated in this matter.
There is a site hosted on a remote debian dedicated server, proxmox is installed on this server (as I understand it, this is a virtual machine, like VMware) in this virtual machine some other qemu virtual machine is displayed, inside which the site is already spinning!
The big question is, why is it so complicated? Why can't you just put everything natively on a remote debian? Of the pluses, I only see that you can quickly roll back to old images ...
And the second question is how to get into this qemu machine?) Because to be honest, I have not come across virtualization products on linux like systems until now)
I would be very grateful for an excursion into the world nix)

Answer 1

Proxmox uses qemu.
A virtual machine is needed for security, sharing network resources, file system. It is easier to backup, clone, transfer between servers (cloud).
There can be many virtual systems on one physical resource.

Answer 2

It is also the isolation of the environment, as well as security