All those things you mention don't affect the user's first experience on your site, you're right: you can use plain JS, ignore clean code practices, have no unit tests, and use the frameworks you're most familiar with even though they don't quite fit, and still start a successful service.
However, they all come into play when you start to evolve your website or service. TypeScript makes it easier to refactor your code when it gets complicated. async/await lets you serve more users. Clean code practices lets you onboard more developers easier. Unit tests and end-to-end tests mean you can iterate more quickly without worrying about breaking existing functionality — something users definitely do care about — which makes it something you should care about too, if you want to keep them around.