The U.S. Chess Federation piloted a 175-move draw rule in the fourth edition of its Official Rules. This interesting rule ended a game automatically after 175 moves, whether or not either player had claimed a draw. (The rule also included some verbiage regarding a particular kind of chess clock, but it is not clocks that I ask about today.)
In the fifth edition of its Official Rules, the U.S. Chess Federation abandoned the 175-move rule.
I liked the 175-move rule and was sorry to see it go, since it lightened certain burdens of subjective judgment and of overextended hospitality from the shoulders of a tournament organizer. I suppose that someone else must have disliked the rule or it would not have been abandoned, but at any rate, is there an interesting story behind the abandonment of the rule?
There was this (PDF) at the time, but it did not explain much.
UPDATE AND APPENDIX
@AndrewNg has given an interesting, informative answer; but an answer to a slightly different question than the question I had meant to ask. At the risk of so long an update that few may read it, let me clarify.
Insofar as I have correctly inferred its purpose, a hard limit on the number of moves in a game exists to protect the interests less of the players than of the players' host (the tournament organizer, hall owner, etc.), without stranding the host in the unfair, distasteful position of having to interject a subjective, third-party judgment into the game. Examples of potentially relevant games include Nicolic v. Arsovic, Belgrade, 1989.
Of course, it is possible that I have misunderstood the rule's purpose. The reason for my understanding however lies in the crucial difference between the 50- and 175-move rules: the 50-move rule takes effect only when one of the players chooses to invoke it (which the aforementioned Nicolic and Arsovic declined to do); whereas the 175-move rule automatically takes effect, without consulting anyone's subjective opinion in the matter.
In short, the 175-move rule prevents the unlikely but nevertheless mechanically regular (and possibly indeed sportsmanlike) play of the game of chess from forcing a mechanical irregularity when the host's patience runs out.
Another, related purpose of the rule -- a purpose explicitly mentioned in the fourth-edition rulebook -- was to relieve a tournament director of the burden of adjudging "insufficient losing chances" in certain technical circumstances.
I admit that, like @AndrewNg, I too doubt that it was ever the rule's purpose to guarantee that every, theoretically forced mate could be carried to its infinite conclusion. Indeed, like the 50-move rule, a 175-move rule if enforced becomes a new, mechanical constraint on the theory of the game; such that -- per theory under the rule -- 176-move mates simply no longer exist.
Maybe the new mechanical constraint on the theory is precisely what the fifth-edition rules committee did not like, but I cannot substantiate such a guess. Thus the question.