That's why the ITC is so relevant here: it is relatively quite speedy compared to regular patent trials, and have the power to issue injunctions against imports (which is partly why it was relied on a lot during the smartphone patent wars.) So you may not collect damages from Chinese companies, but you can completely block their infringing imports into the US and deny them US revenue.

Why isn't Amazon liable?

Yes and no -- filing patents is quite affordable (probably outdated info, but I recall average costs for drafting and filing was ~10K / patent, most of the costs being related to the drafting rather than filing.) Compared to all the other capital investments required for hardware startups, these costs are negligible.

But you're totally right that enforcing them is extremely expensive, slow and risky.

That said, Roomba isn't exactly a startup but wasn't a tech giant either, and did enforce their patents often.

And especially against imported infringing products, the ITC provides a much cheaper, faster mechanism to get protection via injunctions.