I don't know anything about the history of subsequent pins, but the original pin was an aid pin that turned into a very convenient protection piece.
In the "immaculately clean climbing" period before cams, that placement either couldn't replaced by a nut, or else the strenuousness of arranging, say, opposed nuts made the prospect extremely unappealing, requiring a level of endurance and skill needed for climbs a full grade harder.
And so the pin survived and became a "feature" of the route, which would certainly be harder (and scarier) if the leader had to fight to get a cam in at that spot.
Now that cams can be placed there, I think the pin should go, returning the route to the level of difficulty nature intended. But I suppose there are too many people who like the route in its present form for that to happen.
Another pin that absolutely should go is the pin over the roof on the second pitch of MF---there's really no excuse for that one.