Note that this is not the end of contrats. This is a minimun viable start that they intend to add to but the missing parts are more complex.
Exactly. People stopped using Ada as soon as they were no longer forced to use it.
In other words on its own merits people don't choose it.
Maybe Ada's bad, but programmer preference isn't a strong enough argument. It's just as likely that newer software is buggier and more unsafe or that this otherwise isn't an apples-to-apples comparison.
A shoutout to Eiffel, the first "modern" (circa 1985) language to incorporate Design by Contract. Well done Bertrand Meyer!
From my outside vantage point, there seems to be a few different camps about what is desired for contracts to even be. The conflict between those groups is why this feature has been contentious for... a decade now?
Some of the pushback against this form of contracts is from people who desire contracts, but don't think that this design is the one that they want.
Finally, it certainly helps to have a standardized mechanisms instead of everyone rolling their own, especially with multiple libraries.
But like modules and concepts the committee has opted for staggered implementation. What we have now is effectively syntax sugar over what could already be done with asserts, well designed types and exceptions.