Part of the issue was the band's sound, as they were viewed by fans and critics alike as a 1960's-influenced power pop band. Additionally, there were significant artistic differences among the band's members that would lead to the act's demise after only a few short years.
In the U.S., The Tourists barely made a dent in the market -- although their 1979 cover of "I Only Want to Be with You" did chart at #83.
"Don't Say I Told You So" was off the group's 1980 album, Luminous Basement, and was the third (and last) album that the band recorded. The song reached #40 on the U.K. singles chart (the last charting single by the band), while the album peaked at #75. The album was clearly influenced by the emerging new wave scene, but the band's pop image was likely one reason for the breakup.
And in the interest of burying the lead, it should be pointed out that The Tourists were particularly noteworthy as the group that Dave Stewart and Annie Lennox were in before they formed Eurythmics.