Maybe 4 years isn't the right time frame but at some point there were sweeping changes in the language, like futures and async/await, that invalidated large parts of the ecosystem overnight (if you made a bet on a particular ecosystem you would either be stuck at maintaining an evolutionary dead end, or eventually migrate to tokio). It seems that Rust evolution is slowing down though.

Now if the library has tons of dependencies, regardless of language, it's very brittle to bring it unmaintained, because your own dependencies may be expected to interoperate with them. This is actually a plus because with C you may be required to do manual data conversions etc, but it also means that keeping old dependencies is a liability