The reason why all bowlers don’t throw the ball straight is because everyone bowls different. Some bowlers bowl with two hands, some bowl with one hand, some bowl without using their thumb, some bowlers with their left hand and sometimes the oil pattern will not allow you to bowl straight.
I have bowled on some oil patterns where bowling straight was not an option and of you did bowl straight, the bowling ball will never hook. The revs you put on a bowling ball, the more pin action you tend to get which will knock down more pins.
Over time, the lanes will start to dry up so bowling straight can be harder so you will need to move slide over some to get back into some oil. Also if everyone bowls straight, that part will become dry faster so everyone will be move more left or right. As a bowler, you need a toolbox of things that you can do on the lane and this what makes good bowlers when they can bowl anywhere on the floor.