In that time frame, there were *lots* of calendaring options.
It just that all of them sucked so bad nobody wanted to use them. The users all demanded the wonky-ass Outlook calendaring as the only option they'd ever consider, hell to all the others.
I never found the facination with Outlook. Still don't. Its like here, have a program that you'll beat yourself over the head with a brick with, and you'll *insist* its the only one you'll use.