Training/checking roles can be viewed as promotion, rather than roles for people who genuinely enjoy or have a talent for training/checking and improving others. In my opinion that is where the difficulty can lie.
LTCs, TRIs/TREs who view their role as helping you to improve and be the best you can be are an absolute joy, those who take the role because it means they’re “better” than the average line pilot or because it’s the next step on the career ladder are less so. It is the role or the airline’s selection process to find the form