I mean, if you spend millions on developing a game, taking two-three years to develop, surely you try to tackle any risks that might endanger the project. For example, by fixing the price on the foundation of your game, i.e. the game engine.
This is a huge change in the way this game engine will be considered for new games. If now during the development and full lifetime of the game the contract rules can change, gamedev companies will start to avoid these kind of contracts.
With this one change Unity made it so that they can now no longer be trusted to keep the agreed upon contract terms intact for the lifetime of the game.
If only they said this would go in effect for new, not-already-in-development-and-paid-for-game-engine, projects from January 1st, it would have saved them this breach-in-trust issue.