The percentage of people who unlock the bootloader themselves is so small, that Xiaomi couldn't be less worried about them. On the contrary, unlike many other manufacturers, Xiaomi releases the source code and welcomes enthusiasts. The problem is with re-sellers, who unlock the devices in bulk and sell a modified version of MIUI to non-technical people. The longer the unlock period is, the longer the re-sellers have to keep the inventory purchased before they are able to make any modifications. This increases their costs and risks, because they now have to make large investments up-front.
