Why couldn't it?

Even compared with C, assembly gives you minimal guardrails, which makes it harder to write correct programs at scale. Assembly code is also verbose, and every instruction is an opportunity to make a mistake.

An e-commerce web app is going to be a large program that's online and an attractive target. You will need more discipline, experience, and tooling to prevent bugs, including bugs made possible by your choice of language. Assembly opens up a category of control flow bugs that are prevented by structured control flow, like mismatched push/pop. Data corruption is easier than when you work with named, scoped variables.

Because he claims you cannot. Pretty much.