Probably, after the Flood, the Tower of Babel took place. God put them into different language groups. They spread out. Those that spoke French went one way. Those that spoke German went a different way. Those that spoke Spanish went a different way.
Then there's these guys, who are, if anything, worse.
Polish and English are two completely different languages, even though their common ancestral tongue is believed to have been spoken only 3,000-4,000 years ago.
Well, this isn't completely true. A look at a Swadesh List for Polish shows lots of recognizable Indo-European roots, some of which are also present in English, such as "nos" for "nose" and "dwo" for "two".
Ah, I see what you mean. Yes, there's a point at which we simply have to give up. Unfortunately, some linguists don't seem to know where that point is. There are protocols which would allow one to distinguish between coincidences and significant data, but where these are most needed they are rarely used.