The reason is that there were several bricked phones due to the AB partition and fastboot. It left people including me stuck with a fastboot loop. The only resolution was and EDL flash. This is a low level flash that flashes under EDL, direct to storage. It can bypass fastboot and recovery flashes. Unfortunately Xiaomi removed the use of EDL flashing from the masses and only service center staff or some people who managed to acquire the EDL authorisation codes can flash EDL.
This does cost, mine was £23 in his currency but after downloading the ROM I wanted to start from ( Global ) and a specific version of miflash, he connected to my PC with TeamViewer and EDL flashed the Global ROM. I then flashed EU and installed twrp when it was released.
If you really are in a fastboot loop and you cannot get to stock recovery, then this may be your only option and if so, pop on telegram and contact
@*spam*paid*service*. He is the man who can.
This is why no one can give you a free resolution if you really are stuck, but try getting a recovery on first, if you can't then it's an EDL flash for you.