I don’t suppose you work for MS, do you :)
One good reason is that the majority of people in some countries with very
low average income (e.g., UA in Easter Europe) cannot afford to upgrade away
from XP any time soon as this means buying a new PC. Why make it
impossible for them to use Lua?
To be blunt, I think it should fail on XP. XP reached end of the
line already and is no longer getting security updates, right?