why don't runways have a "high-speed" entrance. If planes take less time to get off the runway using the angled taxiway would it also make sense that planed entering for takeoff would take less time if they didn't do a 90 degree turn? An aircraft could start its roll on the high-speed entrance and then fully apply power once aligned instead of using taxi speeds to enter. Something similar to the USAF alert aircraft taxiways.
Mostly for centerline alignment during acceleration. Think about what happens if the plane has trouble turning. On a high-speed exit they can always continue down the runway or hit the brakes harder. But, on departure, an aircraft is rapidly accelerating, making the turn much, much more difficult due to the increasing speed. If you've ever driven a car quickly off an intersection into a turn you'll be familiar with the tendency to lose traction when accelerating in a turn.
