First, as you say, these languages were spoken by very few people. I remember reading not long ago, the obituary of a Scottish dialect spoken in a single villag

First, as you say, these languages were spoken by very few people. I remember reading not long ago, the obituary of a Scottish dialect spoken in a single village. You can't really expect a language with such a small group of speakers surviving the advent of the automobile and the radio for very long. And these languages did not die by a thousand loanwords: the young folk didn't learn them, and the old folk who could speak eventually died. There is also another factor at play here. "Proper" languages (that is, not dialects) have hundreds of years of written material behind them, and this is critical to ensure a language's survival.