If all the guns had the same manual of arms and even shared the same magazines, it might simplify training. However, you'd still need to regularly train to intuitively draw from all those locations.
And to defend against grabs or simple displacement losses from all those locations, simultaneously.
But even simpler than that: There is some very very small, but non-zero, chance that you might be attacked.
There is some very very small (slightly smaller) chance that you might be attacked and can/need to access a concealed firearm to defend yourself against that attack.
There is a MUCH smaller chance, multiplied against those already very small chances, that your primary firearm might be shot empty, or might malfunction, and you need to access a second mag.
And a pretty danged tiny chance that you'd have time and opportunity to successfully do so before the attacker flees or disables you.
You could, maybe, say that you view your (1st) back-up gun as the preferred alternate instead of going to that second mag for your primary gun. Ok. Long odds, but almost everyone at least carries a spare mag, so let's call that an equivalent choice.
But now you're looking at the odds of a)being attacked, b) being able and the situation right for trying to stop that attack with a concealed firearm, c) shooting empty or having a serious malfunction with your primary gun, d) having time and ability to access a backup gun -- all of which are multiplying against each other in levels of decreasing probability -- AND then e) shooting empty or experiencing a malfunction of your SECOND gun, ANNNNND THEN f) having time and ability to access a THIRD gun, and still needing to and being able to defend yourself after shooting empty or disabling TWO firearms.
AND THEN??? A forth gun, of course. It's rather absurd, when you contemplate the chronology and physics of how any scenario where that might all fall together could possibly happen, for an average citizen living in Normalsville, Your State, USA.
Too many options can be bad. It makes you hesitate when you have very little time to act decisively.
And that's certainly true.