I've been told that the reasoning behind this is shady resellers loading unremovable system malware to the system partition (which runs as device admin++) before reselling this to you.

Apparently this is a huge problem in China, where there seems to be quite literally no trust at all on online shopping. This actually does seem to be the case if you try buying devices from any NON-xiaomi-official store Aliexpress shop. They're usually $0.01-$1.00 cheaper, and are guaranteed to be packed with massive amounts of malware. None of which can be pressed "disable" or "uninstall" (greyed out).

They use fake reviews and fake buyers much like Amazon in the west, to inflate their order count and ratings to be sorted above Xiaomi official store