I don't have hard data, but a large part of this is probably ecosystem. TypeScript updates more often and, most importantly, almost every relevant library has T

I don't have hard data, but a large part of this is probably ecosystem. TypeScript updates more often and, most importantly, almost every relevant library has TypeScript type definitions available. Interesting hard data would be the percentage of popular libraries with TypeScript type definitions available vs. those with Flow definitions available. I'm quite sure that would heavily tilt towards the former, though.