Partially because they think that once employees put enough context and rules into markdown files they can be fired and replaced by an online subscription.
The impact of AI on jobs appears to be more in terms of hiring slowdowns: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=5425555
> Following adoption, junior employment declines in adopting firms relative to non-adopters, while senior employment trends remain largely unchanged. This decline is concentrated in occupations most exposed to GenAI and is driven primarily by slower hiring rather than increased separations.
It's that enough execs think it can happen.
No actual evidence is required for that.
But I've started to deliberately constrain myself because of what you describe. Sure, I'm not convinced that it actually come to fruition, but just the realization that this is what they're daydreaming about makes me sick so I've forced myself to only do the bare minimum or less now.