Yes but you don't necessarily lose tenure if you don't publish, no? So realistically the promise isn't that important if you don't really suffer from failing to keep it.

Promise as in showing the potential for future research, not for your promising to do future research.

But yes, it is a gamble, that often fails. But people aren't given tenture just because of what they've done in the past. Yes, it relies on what they've done in the past, but the intent is that past behavior is a predictor of future behavior.