It is not a rule Mike, but it is taking into account that new gyroplane pilots have their minds full. If you think about gyroplane takeoff, it is the most involved procedure among takeoffs in any 2 seat simple aircraft. Pre-rotate, advance throttle but not too much, release pre-rotator simultaneously pulling back, as you roll balance on mains, keep attitude and allow clean takeoff. Yes, to me, you and others after doing it dozens of times it is simple. To new gyroplane pilots it's not. To older pilots, it's one cough away from skipping a crucial step.
I know of at least 7 gyroplane takeoff accidents, having blade sailing on takeoff. One of the common elements among them. Pre-rotated on taxi way and turned on the runway while blades were spinning.
When Greg was teaching me to fly gyroplanes in the beginning and I already had 3500+ hours on trikes and planes with 2000+ as an active instructor, I was thinking this takeoff crap on gyroplanes is too many things to remember because he started pre-rotating on taxiway. I can only imagine a 70-year-old student. I do not agree with Greg teaching that, so I do not teach that. Can I pre-rotate on hold short and turn on runway now and co-ordinate rotor RPM increase during the turn now. Absolutely. It isn't much of a problem but that is now. At the end of the day the proof of pudding is in the eating. When you see so many accidents specially in older new to gyroplane pilots on takeoff having accidents because they are trying to manage multiple things in their head and get overwhelmed, you have to make it simple.
Do you have to have a clear shot at the runway and do not take it till there is a clear shot. Yes. I'd rather them wait than rush it in and splash.