Its because the name is just chess.com and nothing else, people are more likely to search chess than lichess for example
It's not just the name. The current owners bought the domain out of a bankruptcy auction in 2005.
The prior owners also were selling a product called Chess Mentor.
They were evidently unsuccessful.
And how do u know that?
having chess as the name of the site makes for much easier searching. That is a big reason why USCF has rebranded itself as USchess.
That was confusion due to the US Cycling Federation having had uscf.org as their domain.
USCF searches can also include an investment firm and the slightly rearranged UCSF (University of California - San Francisco)