From my experience in the military, I have seen this all too often. It's one of those design issues common to science fiction shows. We love to show you the technology (the sideways-moving turbolift; awesome, right?) but we neglect to show you the stairwells. (Stairs? Who uses stairs in the future? Um, everyone with legs, sir.)

Most likely there ARE stairs, but we rarely see those parts of the ship. Engineering is one of the places we occasionally see stairs.

On a real Navy ship, stairs are condensed, tight and often part of the water containment protocol used to seal separate decks in the case of hull breach. Note the hatch and wheel used to seal the deck during emergencies. Here is an example of what a stairwell looks like on a Naval vessel:

No, it is not sexy. I imagine it wouldn't be a whole lot sexier on a starship, so we just assume there is a means of getting from one part of the ship to another when the turbolift is out.

This appears to be the Federation equivalent. Note the door able to be sealed preventing decompression between decks:

It's a tight fit, so I assume there are lots of these to accommodate the difficulties of navigating them.

Enterprise D was a large craft nearly 700 meters long and crewed normal families as well as military personnel.

It is more than likely the civilian crew did not use the Jeffries Tube system to get around since they lead to secured sections of the maintenance aspects of the starship. Stairwells of one sort or another had to exist to support non-military personnel.

As strange as it may sound, stairs on a contemporary Navy ship are efficient especially if there is a process for moving up or down during emergencies. There are designate up and down ladders during such emergencies to speed crew to their battle-stations.