The answer to all questions: marketability and profits! The movie plot wasn't intended to sell to gamers; we're small fries to movie studios. To them, the real money is in the non-fan casual mainstream audiences, which is why so many game-based movies are so different from the games and offer very little "fan service."
99% of game-based movies flop faster than a movie with Madonna in it, and the first TR movie did at least make decent earnings. Considering the atmosphere at theaters for game-based movies, they're lucky to even have made any money off of the first one, and were pushing their luck with a second one.