Why does my computer boot faster when rebooting than a cold startup?

I'm using Boot Racer and it shows that Windows 10 loads more slowly after a fresh startup than during a reboot. I tried doing a clean boot, but to no avail. I also tried comparing Fast Startup enabled and disabled, and it made no difference. It's only a 10-second difference (20 seconds compared to 30 seconds), but it does this all the time and I'm curious as to why?

I'm using a Samsung 840 Pro SSD, but loading a lot of stuff, like my Outlook email browser.

It's usually about the drivers, reboot keeps some of them loaded but cold boot has to start from the beginning with the HDD platters not spinning. "Back in the day" of MS-DOS and Windows 3.xx the HDDs were slow so a warm boot/reboot didn't allow the HDD platters to fully spin down so the computers did boot faster. The slowest HDD I ever worked with on a PC was the 5.25" Quantum drives, slow and noisy.

It is also related to RAM. While shut down, memory is emptied fully, but when restarted it keeps all of its content and the computer doesn't have to write everything on it again, just read what's already stored and can be used again. Like drivers, CPU cache, etc...