AFAICS the Typescript types ecosystem is bigger simply because Typescript has been advertised to devs coming from a background of a statically typed lang, and they cannot imagine not using types, thus they drown in them.
Flow on the other hand appeals to those that want types primarily in their own codebase, and come from inferred/dynamically typed langs, where you gradually add static types starting with key sensitive parts in your codebase e.g. Erlang http://learnyousomeerlang.com/types-or-lack-thereof
Definitelytyped is frustrating; sometimes they have the type definitions sometimes not. Often the definitions are out of date and new ones are not available. Sometimes I feel that it's better not to use it at all... That way I don't have to think about it.