You can optimize a lot to start a Linux kernel in under a second, but if you're using a standard kernel, there are all manners of timeouts and poll attempts that make the kernel waste time booting. There's also a non-trivial amount of time the VM spends in the UEFI/CSM system preparing the virtual hardware and initializing the system environment for your bootloader. I'm pretty sure WSL2 uses a special kernel to avoid the unnecessary overhead.
You also need to start OS services, configure filesystems, prepare caches, configure networking, and so on. If you're not booting UKIs or similar tools, you'll also be loading a bootloader, then loading an initramfs into memory, then loading the main OS and starting the services you actually need, with eachsstep requiring certain daemons and hardware probes to work correctly.
There are tools to fix this problem. Amazon's Firecracker can start a Linux VM in a time similar to that of a container (milliseconds) by basically storing the initialized state of the VM and loading that into memory instead of actually performing a real boot. https://firecracker-microvm.github.io/
On Windows, I think it depends on the hypervisor you use. Hyper V has a pretty slow UEFI environment, its hard disk access always seems rather slow to me, and most Linux distro don't seem to package dedicated minimal kernels for it.