Because of that prototypes should be small - no more than a week or so worth of effort. Anything larger means it will take even longer to rewrite it from scratch which management will never like and is overall just a waste of time. Most of the time you don't actually want a prototype - you want a MVP written in the language of the final project as it will become the final product.

Really the only time I would write a prototype in a different language then the final product is when you don't yet know the language you want to (or more likely, need to) use or you know another language vastly more than the target language. The time saved by the language is often just not worth it overall when you are reasonably competent in both languages.