That's because when you learn a foreign language correctly, you start with boat or ship and add subdivisions of those as your command of the language improves. You can fuck up a lot and still be understood too. People who are native English speakers have a tendency to get hung up on using languages correctly instead of just using them. The question "when you boat go water?" is the same as " when does your yacht set sail?" But much easier to say when you dont have a large vocabulary.
Also having a bunch of people who understand your native language doesn't incentivise you to learn. It's something I notice a lot with people who come over from Eastern and central Europe. Some of them will have almost no vocabulary and then a couple of months later can hold a conversation and are pretty fluent within the year. Whereas a Brit can live in Spain for a decade and stil only know a couple of sentences in Spanish.