It does not matter and it would only hurt your feelings.
This is not solely about you or them its a match between the two.
Therefore its the same thing as asking a girl "why dont you like me? I am a such good guy". There simply are no answers for this.
Btw, one of successful dating advices I remember was to create a detailed realistic image of a partner beforehand and compare/ask about it on a date. No need to make it strict, but this simply makes you aware of what you want (or not) in a relaxed state instead of allowing your sub to decide under pressure or effect of the moment. Sounds reasonable and pretty sure if true then that applies to jobs as well.
I agree there are always answers, but nobody should be obligated to give them.
"Because I don't want to" should be a perfectly acceptable answer to any question of why we're denying a request. Assuming, of course, we are familiar with the consequences of not completing the request and okay with them.