It was the same time pretty much when we did have the tri-series too TBH. But as I say, that's just the way it worked-out, it's not via planning that way I don't think.
Ergo:
In 2000 and 2001, the pattern was two-Test-series, ODI tri-series of 10 matches, five-Test-series;
In 2003 and 2005, it was two-Test-series, ODI tri-series of 10 matches, three-match bilateral ODI series, five-Test-series;
In 2002 it was three-Test-series, ODI tri-series of 10 matches, four-Test-series;
In 2004 it was three-Test-series, ODI tri-series of 10 matches, four-Test-series, three-match bilateral ODI series, Champions Trophy;
In 2006 and 2008 it was three-Test-series, five-match bilateral ODI series, four-Test-series, five-match bilateral ODI series;
In 2007 it was four-Test-series, three-match bilateral ODI series, three-Test-series, seven-match bilateral ODI series;
In 2009 it's two-Test series, three-match bilateral ODI series, Twenty20 World thingy, five-Test-series, seven-match bilateral ODI series.
No three summers have ever been the same, and only once have two consecutive ones been so. I don't think there's any specific planning to have any one thing in one place TBH. Though I really rather wish there was. I wish ODIs were always midsummer, I hate this latest fad for September ODIs (though it does at least mean there's some point to playing day\night ODIs in England). And I also hate the way there's just more and more every summer. Ideally, the international summer would run from mid-May to late-August.
Of the above templates (there's no way we're going back to the 1998-and-before pattern, and nor do I wish to see that happen) the one I liked best was 2001. Just one set of back-to-back Tests, ten ODIs, and seven Tests. Would still be perfectly workable.