Because slaves were property and not legally persons and Indians were born of independent nations and therefore not under the jurisdiction of the US government.
The simpler answer is that the founding fathers did not want slaves and Indians to be citizens.
Why were the children of German citizens (who were also born of independent nations) not treated exactly like Indians? I would point out that Indians born *IN* American cities were excluded from citizenship, while Germans were not.
I will also point out that many slaves were manumitted and thereafter became citizens who could pass on their citizenship to their children.
The simpler answer is that the founding fathers did not want slaves and Indians to be citizens.
There were plenty of Black citizens during the Revolutionary war era. Crispus Attucks comes to mind.
No, that answer doesn't suffice. Why would Manumitted Slaves be able to obtain and pass on citizenship to their children, when those held in bondage could not?
Even after the slaves were freed, they were still not considered citizens until AFTER the 14th amendment granted them citizenship en masse. Indians were still a No-Go at this time.
There is something more going on here than a mere "born on the soil" requirement.