Because their income comes from advertising. Because the economy sucks in general, companies in all industries are being more careful with where they spend their marketing budget.

You can see this reflected in the revenue of other advertising companies as well such as google and meta.

The owner of Amazon was the prime beneficiary of VC funding to tech companies, because oftentimes a large chunk of that went for AWS. In that gold rush, Amazon was the one selling shovels.

The gold rush is now over, for a while at least, so Amazon is probably seeing a lot of their big AWS customers cutting back, or in some cases disappearing. Essentially, AWS is in the same position as SVBank. If your money comes from lots of tech startups that don't want to have their own infrastructure, and didn't used to need to worry about cutting costs, but now they do, then you can see big "outflows" (except unlike SVB it's more decreasing revenue).

If they laid off 400 employees, it’s probably because they could afford to (nice way of saying: they were not necessary to keep the business functioning), likely a bet on innovation. As the economy struggles and the prospects of such innovation happening seem far, it makes sense that even a big company like Amazon may choose to cut their losses.

Amazon (like every other big company) has raised billions with bonds that they will eventually need to refinance at higher rates.

Amazon needs to provide attractive returns to shareholders just like a unicorn. If you $AMZN is not up 5% YoY, then sell it and park it in a 6 month T-bill or I series bond. And as holder of $AMZN, I can tell you that they are definitely not up 5% YoY, let alone the 15% that they generally try to get to.