The definitive answer to this question may always remain with the bees. However, we know of certain physical limitations which can cause this situation to develop. The main one being, no young larvae of the proper age to feed royal jelly to. And the cause of this can be traced to at least a few known reasons. The queen bee doesn't always lay eggs consistently in time. True, during the summer months she's pretty consistent and busy doing this. But in the Spring and Autumn, it's not uncommon for her egg laying to be influenced by temperature/weather swings and she may shut down and stop laying eggs for a few days. Normally, she's still producing pheromones strong enough to alert the colony of her presence and suppress egg laying by worker bees (etc). However, if she's an old queen and her pheromone production isn't what it used to be, it may be that prior to her death, the colony interprets her lack of egg laying as just part of her normal cycle and thus they're not motivated to identify a "replacement" queen larvae until it's too late.

There also have been reports of supposedly queenless and egg-less hives somehow managing to queen-right themselves when all hope was gone. The theory goes that some manner of a 'robber bee' goes and steals an egg from an adjacent colony and actually flies back to the queenless hive with it. It makes for a great little tale but remains very much unproven.

I once had a permanent observation hive that had two queens in it all Spring and Summer long - a mother / daughter queen combo. Pretty unusual. The older (mother) queen had been the sole queen, the year before. I had marked her with yellow that year. The following Fall, I found both her and her daughter (which I had also marked earlier in the Spring, thinking a supercedure had taken place) crawling around in the hive. The mother queen had a much pronounced smaller body/abdomen and just a few attendants around her. The daughter queen was a nice, big healthy-looking queen with a larger number of "court" attendants around her. The colony had obviously existed this way for several months.

We like to think that when a colony realizes it has lost it's queen it immediately gets to work replacing her. But unfortunately, that's not always possible. And even when a replacement queen has been raised, if she gets eaten by a bird or a dragonfly on her mating flight then the colony is still doomed. Many things can (and do) go wrong and we probably don't have a very full understanding of all these possibilities.

tx, txbeebuy, you bee (as always) a great source of information.

Yes, and also....I'm thinking of many diseases that can come along and no matter as how hard they try raising a new queen, it just doesn't work when you have lets say... American Foulbrood.

That's right. Only a healthy hive will right itself.