Hikaru Nakamura's Forbidden Platform
There is plenty of room for all of Chess.com, Chess24 and Lichess to exist.Lichess has the best platform to play on and is free to use.Chess.com is a business. As such they want to earn money.
However, without a large, online chess community there will be no subscribers.
The amount of effort chess.com has made to sponsor events, streamers etc.
is tremendous.Making a living as a chess professional is tough. 
Streaming/YouTube has opened the field somewhat: it is no longer
required to be in the world top 20 to make a living in the field of chess.The Chess24 initiative is without doubt inspired by Chess.com.
Chess24 gives yet another way for chess players to earn money.
Via Chessable (owneed by Chess24) players can sell chess online book/booklets.If Hikaru has a clause in his contract with Chess.com, that he can't play on Lichess - then the just can't play on Lichess. That's simple.Would Nike be happy if Portugal’s Cristiano Ronaldo suddenly appeared in Adidas shoes?It works the other way too: Wen did you last see Magnus play on Chess.com?
[I am aware that Magnus as owner/investor in Chess24 makes his own rules - and plays on Lichess]