Yeah, the author wants a story saying there wasn't enough continuity between scenarios or motivation to continue, but that was a non-issue for me personally. It's been many, many years, but my memory is that while RCT didn't have a completely open sandbox like TT to boot, each scenario was effectively its own sandbox with restrictions that made them interesting. New rides became available you progressed, and each park enabled creativity in different ways. When you finished all of the scenarios, I believe there was a completely open sandbox that became available, and that was like a nice reward. There really was no need for a story, and I think that would have detracted.
> It's been many, many years, but my memory is that while RCT didn't have a completely open sandbox like TT to boot, each scenario was effectively its own sandbox with restrictions that made them interesting
Also a very long time ago I played it, but I seem to remember that you could continue any scenario for as long time as you wanted after completing it, you didn't need to exit the scenario once completed. Maybe I misremember? If not, that'd basically mean every scenario is also a sandbox once the goals were completed.