Fear of what might be causes this including avoidance of possible pain. Aikido in my mind should be teaching how to face, harmonize with, be in present time. Thus I am not led by false tap outs.
I have very flexible shoulders and can often accept a nice long pin as a welcomed stretch. However sometimes the person is unwittingly holding my hand, albeit lightly, in such a way that my very arthritic thumb, which is having an exacerbation, is in complete agony.
I asking the person about their experience of what happened after the fact and coming to an agreement about slowly working through their comfort zone. But it is incredibly presumptious to think you can read what, how, why and how a person is tapping and overrule their judgement.