Lots wrong in your comment.

1. Even if one assumes that someone claiming AI will reduce the need for workers decrying population decline is hypocritical, your complaint falls flat because you haven’t shown it’s the same people making the same claim. You’ve fallaciously used the term “leaders” to imply they’re a monolith but “leaders” almost certainly have different views. Some believe AI will reduce jobs and are not decrying a population decline while others believe AI will not reduce the workforce and are decrying a population decrease.

2. Of course one can decry a shrinking population even if one believes we don’t need as many workers. Heck, one can decry a shrinking population even if one believes the population should be smaller depending on why the population is shrinking and how much it’s shrinking.

For example, if the population is shrinking by 2% but if jobs will reduce by 1% that could be bad. If population is decreasing an appropriate amount, that could still be bad if it’s decreasing because of say a deadly pandemic killing people off. Or the population decrease can still be bad because the decrease is in the kinds of people the future economy needs.

3. Just because a smaller workforce is needed doesn’t mean a population decline is a good thing. If that smaller workforce can provide significantly greater output a larger population is a good thing so more people can enjoy the benefits of that greater output.

4. Finally, even if population decline is a good thing thanks to AI and the rate and nature, etc of the population decline is perfect it could still be a bad thing if the timing is wrong and the population decline happens way before AI starts killing those jobs.