This should be obvious, but you also had a different child.
Our oldest child wouldn't sleep until we got him not only out of the bed but the bassinet all the way out of the room.
Our second child slept like a baby pretty much whenever.
Our third did fine in the bassinet, but now that she's older and transferred to the nursery she wakes up if even the slightest bit of light comes in through her door.
Kids are wildly different from one another from a very young age. I wouldn't assume that your cosleeping is the cause of your having fewer sleep troubles. If anything it might be the reverse.