Famous or rich families back in the 1700’s and before might have records and common folk want to be related to them so they take those suggestions online without one iota of proof.
We can’t trace the King name past Katherine King b1778 but the Ancestry site will take it back to all sorts of people based on hunches.
It makes it more interesting for people to talk about. The Ancestry site saying one's lineage is traced back to the Magna Carta better than saying they think a family line can be traced back to some guy who got off a boat in New York during the 1840s from somewhere in Europe.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)