I have a theory on this. Is it possible that rematch is a very "American" thing? On chess.com where player nationality is shown in the interface I've noticed (I think) disproportionate rematch requests from American players if they lose. I am pretty relaxed and tend to accept such requests, but I never ask for rematches myself. So game theory allows a closely matched player to always beat me in a match by simply continuing to request rematches while they are behind on the match score. This actually happens quite often (anecdata I know). Summarising my theory is that rematch requests are often a reflexive response to a loss, but more so in America than Europe. Furthermore lichess tends to be a more European site, chess.com more an American site. Hence more rematches on chess.com than lichess. Just a theory.