Why do top GM's "retire" from chess? After Kramnik's recent announcement, Nakamura also said in a chess.com interview that he will retire from chess at age 40.

I am curious why a super GM feels the need to "officially retire" from chess (or a format of chess). Why not just stop playing but keep the door open for future events? Who knows, maybe you'll feel different after a break.

To be clear, I am not asking for speculations specific to Kramnik or Naka's mindset. I want to know what concrete, practical reasons there may be for a top GM to announce retirement, like sponsorship or contractual reasons as an example.

Update based on comments and whoever voted to close: I'm specifically not asking for guesses or opinions, but for insight from someone who have knowledge of a super GM's unique situation (be it legal, social, practical or otherwise) to elaborate why it is beneficial to announce retirement rather than simply stop playing.
I don't know about the practical reasons that you suggest, but I imagine retirement is a way to tell your fans and the world "stop bugging me!". :-) Super-GMs probably retire when they feel they are past their peak and would rather retire at the top of their game than have the world see them decline.

That said, retirement is not irreversible! For example look at Kasparov, who "retired" in 2005 and yet has reappeared in tournaments from time to time: https://en.wikipedia.org/wiki/Garry_Kasparov#Retirement_from_chess.