I had heard these kind of things about Lewis too! Leaving hundreds of millions on the table and walking away is not an easy thing for anyone, even if they already have hundreds of millions in the bank.
I remember reading an interview with Nico Rosberg where he said that he left over $100m on the table in commercial opportunities by deciding to retire after winning the championship in 2016. However, he knew that he had given absolutely everything that season and did not think he could do it again.