The "real" reason, if there even is a single one, is the regulations of the time.
Ships in the era of the Titanic were physically much larger than they had been a generation before, and regulations hadn't yet caught up to what that meant for seaworthiness - as an example, one of the older-generation ships had struck an iceberg a decade or so before the Titanic's fateful voyage. You've not heard about it because this ship, with proportionately much thicker hull plating compared to the mass of the ship and a different shape that kept the impact away from the waterline, essentially bounced off without major damage.
Titanic, with her vast mass - 50,000 tonnes, more than double the size of the White Star liners commissioned only ten years earlier - slammed her flat sides into the iceberg, and her hull, while thicker than that of her earlier sisters, was still only 3/4 of an inch plate, driven into the iceberg with 50,000t of force behind it.
Regulations of the time were written with collisions between ships in mind, one driving bow-first into another somehow. The ship that rammed the other, per regulation, would stay afloat due to the strong bow bulkheads designed for this, and, if the damage to the other ship was significant enough to risk that vessel, both ships would combine their lifeboat flotillas to transfer passengers over to the ship with the damaged bow, which, thanks to the collision bulkhead, would still be seaworthy.
That's why Titanic was short on lifeboats, and why she was incapable of dealing with having a section of her side carved away.
The "real" reason, if there even is a single one, is the regulations of the time.
Ships in the era of the Titanic were physically much larger than they had been a generation before, and regulations hadn't yet caught up to what that meant for seaworthiness - as an example, one of the older-generation ships had struck an iceberg a decade or so before the Titanic's fateful voyage. You've not heard about it because this ship, with proportionately much thicker hull plating compared to the mass of the ship and a different shape that kept the impact away from the waterline, essentially bounced off without major damage.
Titanic, with her vast mass - 50,000 tonnes, more than double the size of the White Star liners commissioned only ten years earlier - slammed her flat sides into the iceberg, and her hull, while thicker than that of her earlier sisters, was still only 3/4 of an inch plate, driven into the iceberg with 50,000t of force behind it.
Regulations of the time were written with collisions between ships in mind, one driving bow-first into another somehow. The ship that rammed the other, per regulation, would stay afloat due to the strong bow bulkheads designed for this, and, if the damage to the other ship was significant enough to risk that vessel, both ships would combine their lifeboat flotillas to transfer passengers over to the ship with the damaged bow, which, thanks to the collision bulkhead, would still be seaworthy.
That's why Titanic was short on lifeboats, and why she was incapable of dealing with having a section of her side carved away.