When an object is being changed via MAXScript, 3ds Max will try to update the changes in the viewports as soon as possible. When the changes are many and done quickly in a loop, redraws should be disabled until all changes have been done.
You can use the with redraw off() context or a pair of disableSceneRedraw() and enableSceneRedraw() calls to speed up you code. The former method is the preferred one.
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