Dynamic language does not make you more agile, it makes changes more risky and refactoring harder.
However, large part is that for frontend, static languages are just getting there. You need not just language, but also libraries, tutorials, tooling, IDE and so on and so forth.
Typescript nor flow does not absolve you from the need to learn javascript and web in general. If you are working on your first bigger project and still learning good techniques, architecture and concepts, css, having to also learn typescript or flow syntax on top of it off-puts people.
However, large part is that for frontend, static languages are just getting there. You need not just language, but also libraries, tutorials, tooling, IDE and so on and so forth.
Typescript nor flow does not absolve you from the need to learn javascript and web in general. If you are working on your first bigger project and still learning good techniques, architecture and concepts, css, having to also learn typescript or flow syntax on top of it off-puts people.