Well, loose typing allows for far faster prototyping. I know some people will debate me on this, but mixing int and string in an array or returning an object or a string is far faster than going the 'proper' way. It's not great, but it gets you started earlier and that's a big point.

Another thing is that it's extremely easy to migrate from vanilla JavaScript to Typescript. You simply add a compile step at first, which breaks nothing, and then you slowly move your js files to ts while still being able to cross use them. I've migrated a ~10k LOC app and it was a breeze - whenever I needed to touch a module, I simply took the 5 minutes to make it TS. Whenever I touched a function, I added the type parameter. Being able to slowly convert a big app without ever having a major breakage or a massive change is something extremely valuable and rare (looking at you, `async`).