Because Olympic had an enclosed B Deck promenade while Titanic and Britannic had not.
If I remember right there were plans in the 1920s to enclose part of the A Deck promenade on Olympic but that idea was dropped again.
Great article Mark. I totally agree, and have written myself that, the idea of enclosing the forward A deck, was in fact due to the loss of enclosed promenade decking for the first class, who could get as much open air promenading they wanted on the boat deck, though deck chairs were apparently not allowed, so there would be little deck chair open promenade space, if this matters. Another point is written in the notes by Leonard Peskett who states that B deck proved to be unpopular. This being the case, with the expansion of the popular restaurant, along with the creation of the reception room (which proved so popular for the 1st class dining saloon on Olympic), it seems that they did away with the unpopular B-deck in favor of what was popular- aka more room for other activities instead of 3 decks (boat, A & B) for promenading.
PS: Since we are on the topic, in the book 'Titanic Legacy of the World's Greatest Ocean Liner', (page 192) there is a set of deck plans that show the locations of the promenade chairs for A deck. Unfortunately the image is small and unreadable. Does anyone know if these plans, in a larger format, have been made available?
My info came from Leonard Peskett's notes which reads:
The coach top over lounge was used by a few [passengers] for games, but the boat deck was not used much as a promenade and deck chairs were not allowed there.
A first I thought maybe this was due to the chairs possibly being swept off deck, but looking more onto this, Titanic: The Ship Magnificent reads (pg. 35 & 37):
The Edwardians did not like to maneuver around deck chairs, and serious promenaders liked to have an area reserved for just foot traffic. Promenading was a popular pastime in Titanic's era, and is why deck chairs were confined to A deck in First Class, and the after end of the Boat Deck and B Deck for second class. Although the occasional deck chair appears in photographs of Olympic's Boat Deck, this was the exception.
An interesting article in 'The Bookman: A Review of Books and Life' Vol. 20, September 1904 – Feb. 1905, says of the Harland and Wolff built Amerika and the Vulcan Shipbuilding Works' Kaiserin Auguste Victoria, “A most welcome feature will be the three great promenade decks of enormous length and width, one which will be reserved exclusively for promenading, while the others will be used for the placing of deck chairs.”
Ignoring the support strut holding up the railing, and focusing on the round-bottomed bin and the dark device behind the man's leg, it looks lo me like a fire hose or line. If it's beside the crane, then likely it's lines or straps for the crane. Judging from the flat-rope look, the round bottom, and the overall size, and that the dark object may be a pump or fitting, I'd say it looks a lot like a fire hose.
If this is the case, and no doubt it is, one wonders why they stuck with Titanic's enclosed promenade scheme, which was in-and-of itself a response to feedback from Olympic, for Britannic?
It just seems prima facie that if B deck was unpopular on Olympic, part of that reason might be that B deck was not enclosed; however, if White Star et al. decided that this was not the case, and that passengers would rather have the other amenities made possible by not enclosing the promenade on Olympic, they would not have made alterations to enclose the deck on Britannic.