Writing code ≠ maintaining code someone else has written. Duck typed code relies in general in implicit behavioural assumption on how the values you're receiving should behave, and it's much better to be the one making choices than the once trying to understand them.

I'm not arguing that it's not possible to do it; I just think that it requires a bit of extra steps and care to document which assumptions your code takes and how it behaves that could be more meaningfully described by a statically typed language. But these are just my 2 cents.