But one could argue that they've often had the opposite effect: Indurain and Armstrong for eg often had no incentive to attack in the mountains because they gained so much time in the TTT and/or first ITT, so they just had to ride defensively to protect their gains or to limit their losses, which they knew they'd more than make up for in the final ITT. I'm generalizing quite a bit of course, but wouldn't racing back in the time of Indurain and Armstrong have been more interesting if they too had to go on the attack in the mountains rather than just "winning" the Tour via the TTs? Evans, too, for that matter. Contador's a different story, of course, he just attacks when and where he feels like it.
But having said all that, I understand why there are TTs and I understand why there always will be, I just find them to be -for lack of a better description - disruptive to the flow of the GC and the GT as a whole. I also know that doesn't make a whole lot of sense, but there it is