Mining enough to alter the orbit of the moon would require a pretty ridiculous amount of time and effort. Much more than our global mining efforts combined and multiplied and on a timescale of thousands of years.

And we only have to launch a few rockets, enough to set up a self-sufficient base which can then produce more rockets and fuel from resources on site. Not to mention it’s much easier, and even feasible with existing materials, to build a space elevator on the moon.