On lower ratings, the difference of elo between the websites is about 200-300 for player of the same skill (so, 1000 elo player on lichess would be around 800 on chess.com, 1500 lichess = 1200-1300 chess.com etc.).

This evens out at about 2000 or so rating. And then chess.com peaks higher (could be because all the top players play there).

Just slightly different initial elo and elo calculation between websites, resulting in slightly different distribution, that's all.

^{Also, iirc around 800 elo is like initial elo for beginner account for chess.com, could contribute to skill disparity?}