Why the bottom would fall out is easy. It wasn't attached properly to withstand whatever the user was doing with the case.
Some people just stick a piece of wood on the leather and put some small thin nails in through the leather and that's it.
Others will glue the wood in and use the small nails.
Some will use wood that is very thick so that it offsets the pressure on the nails.
Some use barbed nails, most don't.
Some bond the wood to the tubes using only glue.
Some bond the wood cap to the tubes using dowels. Some do this with nails (us).
Some try to do it with insulation silicon.
Some people put foam rubber in the bottoms of the case to dampen the impact of the cues, some don't.
But the bottom line is that if the bottom falls off during the course of normal use then the case was improperly built.
The way I feel about it is that the case ought to be able to survive repeated falls from about six feet without the bottom being damaged. People put the cases down fairly hard sometimes without realizing it, they drag their cases (inexplicable to me), they drop their cases a lot, they throw their cases in the car, in the parking lot, across the room, they slam their cues into their cases when they lose, and cases get generally bumped and jostled.
Chas Clements once told me he builds cases as if someone's life might depend on it because someone's life might. This might sound like overkill for a cue case but I think we all have the expectation that the primary function of a case is to protect the cue and obviously cases where the bottom comes off easily is not doing the job.