score:5
The feature you indicate in the left-hand picture is called a cage.
In the case of the Titanic, the crow's nest was accessed by a ladder inside the mast (as noted in your citation), so the mast itself would have acted as a cage, helping ensure the safety of those climbing the ladder to the crow's nest.
As to the wider question of why safety features like cages weren't fitted to most ships at the time the RMS Titanic was built, the reason is simply that Health and Safety legislation is a relatively new phenomenon. The requirements simply didn't exist when Titanic was being designed and built.
You can get an idea of the history and evolution of Health and Safety legislation in the UK from this infographic on the site of the Legislation Update Service. When viewing this, keep in mind that, as a rule, the people making the laws were not the ones climbing the ladders on ships in rough seas or icy conditions in the North Atlantic!
Upvote:5
Working sailors didn't require many of the modern industrial safeguards, as they were taught to work with "One hand for the ship, and one hand for yourself". It's a tradition as old as any old sailor.
For example, this is me heading for the main-top aboard the USCG training vessel Eagle during the summer cruise of 1968.
In more recent years they have adopted the use of tethers for everyone working aloft.