Here are a few hypothetical situations.
1). A stronger coaster was needed for the Chicago market, as Bob-Lo was still a 'player', but Cedar Point has come into its own as the top midwest park. Robert Munger brought Cedar Point up to speed with the Gemini and Corkscrew, and a new marketing campaign was focusing on 'The Amazement Park'. Unlike now where rides rule, but the emphasis is on multi-day stays with the new hotels and Soak City and such. Chicago's Great America hasn't had the luxury of 'name recognition' so early in its history.
2). Zoning. Happens when you least expect it.
3). Company changes. Maybe Marriot realized that the parks had totally different patrons and therefore Chicago was a bit more agressive.
4). Wait, I got it. When PGA built the Grizzly in '86, Taft Entertainment owned and operated PGA. Their parks received this Curtis Summers model at Kings Dominion in 1982, Wonderland in 1981, and Great America in 1986. Kings Island never received a clone of the Coney Island 'Wildcat', since a) the Beast was more than adequate as the lead woodie, and b) a clone of a beloved Cinncinati legend would only bring, well, you know what happened when the 'Twister' showed up in Denver with the locals. You and I could care less where block brakes are, or what color the trains are, but true historians are very critical.
6). Come to think of it, Marriot sold the parks off about 1980 or so. Anything else?
*** This post was edited by Agent Johnson on 12/11/2000. ***