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Cathedral hands date back to the very early 1900s
In fact, Rolex seem to have used them before lume was a thing.
Stonehedge
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When tritium started to get used on oyster case professional models, the designers obviously wanted as much visible tritium on the hands as possible so in R&D the original hour hands didn't have the lattice work, just the lum.
The difference being that these modern day professional models weren't dress watches any more, for the first time ever, people were going diving and and mountaineering and such whilst wearing their watches, the original tritium didn't get make it through testing so the hand was latticed.
The non professional models weren't really seeing much deep sea diving so the hands on the date just etc. did not require as much lum and therefore did not require any structural support.
Antidotes
Basically the Rolex Geneva PR dept. haven't come up with an official theory as such.
It's based around it's functionality to keep the tritium in place and the Mercedes symbol was reasonably aesthetically pleasing.
I've seen a very old prototype hour hand in which the tritium was only halved but at the time the watchmakers still were not happy with the security.
The tritium compound of old was not very good at staying put, it dried out pretty quickly, cracked, got dusty and fell out.
Thankfully lum technology has come a very long way in 40 years and we don't need to worry about surface area like the watchmakers had to back in the day.
The merc symbol isn't needed anymore but will remain as part of the heritage.
Still prefer something like the Tudor snowflake though.