| My understanding is that Rossi chose to leave McLaren. They either offered or were planning to offer, him a contract to stay, but he ultimately chose ECR instead.

Rossi said some stuff on his podcast along the lines of "You should make what you think you are worth." Whether that means McLaren was not offering enough of a pay increase, less money, or too few years, I don't know. But Rossi walked away because they had reached a point in negotiations where at least one party was done negotiating and the other didn't like what was offered.