Wrong question. The right question is: if we need guns to defend ourselves against tyrants - why didn't the Nazi gun bans prevent the Warsaw uprising (or the thousands of other armed resistances throughout their empire) ?
Well, simple, because gun control are for normal situations - nobody OBEYS a gun law by a government that wants to kill you. If the need arises to resist a true tyrant - all the people advocating for gun control right now would acquire guns, join the resistance and fight back right next to you.
But that is, of course, a situation that has declined rather a lot in frequency - out of over 300 countries on earth, such situations only arise an average of once every 3 decades, and sufficiently so to create resistance movements only once or twice a century.
Why sacrifice millions of innocent people every year, to protect against a one in a million scenario you probably won't live to experience, when you don't even NEED to sacrifice them to have the gun if it happens ?