I realize that very likely the answer to this question is likely to be something along the lines of "that's just the way it is", but I thought it worth asking to see if there were some insights that weren't immediately apparent.
In Tokyo, the JR train line called the 山手線【やまのてせん】 seems to have dropped the の from the way it is written. It seems there used to be areas of Tokyo referred to as 山の手 , which was where the elites lived and is in opposition to the term 下町【したまち】(downtown, lower class areas). I hear the 下町 often enough in reference to areas like Asakusa, but I haven't heard anyone use 山の手. The only やまのて I know of these days is the 山手 train line.
There is also an area of town called [御茶ノ水]【おちゃのみず】, where the の is still there, but in katakana. Why not leave it in hiragana...?
So, is there any rhyme or reason to how these conventions of spelling came about? Is there a relation?
Or are they just quirks of tradition that just stand on their own without any rhyme or reason?