>>If other ships were or were not better sub-divided I have no idea <<
By and large, they're not with the notable exception of warships which must be able to survive quite a bit of damage. An Olympic class liner was designed to remain afloat with up to four of it's watertight sections flooded. As far as I know, you won't find a single cruise ship/liner which can meet that standard today. For obvious reasons, shipping lines aren't keen to advertise this fact.
>>but it does not mean the Titanic could not have been better designed using the technology then available.<<
Quite right, they could have been. However, this is far from a gaurantee. Britannic had all of those features you described and sank in less then an hour after striking a mine. The Lusitania had sectioning that would have done any military vessel proud and sank in only 18 minutes. It doesn't help that a lot of the safety features they had weren't even used. The Britannic had portholes open which should have been closed as well as watertight doors which have been found still open going into the engineering spaces.
>>So until a ship can be designed that does not sink all we can ask is that a vessel is built using all the possible safety devices without having to wait for disaster. It is this that I would think is the desire of any traveller.<<
A noble idea in theory, not quite so do-able in practice. Passengers like ships with all the amenities, all the luxuries, and above all, which are easy to get around in even for those with signifigent disablities. Unfortunately, this clashes badly with building ships that have the maximum in subdivision. Such vessels are very difficult to get around in for any but the able-bodied. An unacceptable situation on a passenger vessel where potential travellers vote with their wallets and their feet in favour of the more comfortable vessel.
There are other problems too, not the least of which revolves around crew training and maintainance. Simply put, the crew of a merchent vessel seldom has the sort of time needed to devote to the labour intensive work involved in keeping every single fitting up to snuff, much less the time to train to set everything properly. A military vessel trains in this sort of thing as a matter of routine in their workup cycle prior to deployment and it takes an average of at least a year for them to learn how to do it right. (I'm a retired Navyman...been there done that!)
Seen in this light, it becomes apparant that putting in every conceivable bell and whistle can be and is seen to be more trouble then it's worth, and when you get down to the very bottom line, there is no substitute for good seamanship.
Never has been and never will be.