Everything that the others have said is absolutely true, but I want to point out one other thing.

Several have pointed out that you needed to raise the flop more to thin the field down to 1 caller (or 2 max). Now, obviously, AA has a much better chance against 1 caller than it does against 3 or 4. But there is still another reason to do it and this hand highlights it.

With so many callers, you cannot give opponents bad odds to draw because they will give each other good odds to draw.

Granted when you pot bet the flop, the first caller is only getting 2:1, but the second caller is getting 3:1 and the third caller is getting 4:1. Further, if people have been at the table a while, the first caller may have felt safe in calling because he was fairly comfortable that 1 or 2 others would also come along for the ride.

People usually call this schooling (as in a school of fish). It is great if you have a heavy draw hand and the money is deep. It is awful if you have a hand that plays poorly multi-way.