Fear is my ally
No straight forward answer, as this opens a lot of other questions that everyone else seems to be asking. such as how did they reach ikkyu not knowing or is unwilling to take ukemi, Although the big highfalls aren't necessary, basic falls are. When a student reaches ikkyu in any martial art, then is not the time to try to correct a defiency that needs to be checked in their first few months of practice. Did this person suffer an injury which may somehow contribute to this fear? Or does this problem lie in the realm of the ego? 10 step programs in Aikido as in everthing else require the participant to want to change. or else it is just you wasting your breath and energy when you could be training either yourself or your students who want to learn. In yoshikan and in all the USAF tests I've seen Ukemi is a graded event where you can fail, even your shodan test.