why did the British government cut off the 13 colonies from the Ohio valley in 1763?

Answer 1

The english wanted to controll the migration and eventually settlement of the west. the americans were doing as they pleased and not allowing an orderly movenemt west. They were moving into the Indians land, taking it, fighting them, and causing trouble for the English government. THey just wanted controlled expansion. the Americans were uncontrollable
The idea they were saving the indians and going to deal fairly with them for one second longer than they had to is ridiculous

Answer 2

In the hope that this would keep peace with the native tribes of the area following the end of the wars with France in which those tribes, notably the Iroquois, had in the main sided against Britain.