Why? Writing types isn't that time-consuming... Types will tell you very easily what is expected to be passed to function. Why does it matter so much? Imo in Ruby it's not that common that service calls are deeply nested. In frontend it's opposite. Components are very nested and with all that prop passing sometimes you have search lots of files to understand what's being passed. There are proptypes yup, but if you write proptypes, why not types?
Also data on frontend mostly comes from backend, so many times there is no really good docs for data that is brought from backend. In backend you mostly access 3rd party APIs with docs or your DB, which you can easily access to see what it delivers: )
And I am not even going to mention editor plugins that show you docs with expected types. Much fewer mistakes and easier coding with external packages.